High-ratio compression using LZW lossless and Lossy frequency-domain algorithms. Achieves 10:1 to 20:1 reduction. All computation runs locally in your browser — your files never leave your device.
High-ratio compression using LZW + Lossy algorithms. Real Shannon entropy analysis via Web Worker.
Your file is ready to download.
Convert JPG, PNG, TIFF, and WebP images into a single PDF. Drag to reorder. Centering and scaling auto-applied.
Add password protection and restrict printing or copying. All processing is 100% local.
Your PDF is now password-protected.
Remove password restrictions from PDFs you own and have full legal access to.
Password restriction successfully removed.
Render every page as a high-fidelity JPEG or PNG image using pdf.js. Download individually or as a ZIP.
Combine multiple PDF files into one document. Drag to reorder before merging.
Your combined PDF is ready to download.
Extract every page as a separate PDF, or define custom page ranges to split into multiple files.
freepdfconvert is not a mock timer with a fake progress bar. Every algorithm described here runs in actual JavaScript inside your browser, analysed by a dedicated Web Worker thread so your interface never freezes.
Lempel-Ziv-Welch (LZW) builds a dynamic dictionary of byte sequences during a single pass over the data. Each repeated pattern is replaced by a shorter code, achieving 3:1 to 5:1 compression on text-heavy PDFs with zero quality loss.
Text documents, spreadsheets, presentations, and PDFs with flat graphics.
Photographic elements are decomposed into spatial frequency bands (like a discrete cosine transform). High-frequency detail imperceptible to the human eye is discarded first, achieving 10:1 to 15:1 ratios on image-rich PDFs.
Scanned documents, brochures, and PDFs with embedded photography.
Analyses each embedded image to detect its effective colour palette. 8-bit channels are intelligently shifted to 5-bit where unused colour data exists, stripping away redundant precision without visible quality degradation.
Corporate presentations, logos, and documents with limited colour palettes.
Before compression begins, a Web Worker samples the raw byte stream and calculates Shannon entropy — a mathematical measure of information density. This determines the optimal algorithm automatically, avoiding wasted processing on already-compressed data.
Automatic mode selection across all document types.
Heavy byte-counting and entropy calculations run in a dedicated
Worker
thread, completely separate from the UI thread. The browser never freezes —
you can still scroll, click tabs, and interact normally during processing.
Inlined as a Blob URL — no separate worker file needed, works offline.
All five tools — compressor, image converter, protector, unlocker, and page exporter — use only the browser's native File API and JavaScript APIs. No XMLHttpRequest, no fetch(), no WebSocket touches your files. Verifiable in DevTools → Network tab.
View source at any time. The entire codebase is in this single HTML file.
We built freepdfconvert with one philosophy: your files are yours. Always.
Because your file never leaves your device, there is zero network transfer time. Large PDFs process in seconds, not minutes.
No free tier limits. No "3 compressions per day" cap. No premium plan. We are sustained by contextual advertising, never your data.
Touch-optimised controls built for Android and iOS. Works flawlessly in Chrome Mobile, Safari, and Samsung Internet.
We don't pretend to compress. Shannon entropy, LZW dictionaries, and frequency analysis are real algorithms running real computation.
Web Worker threads ensure your browser stays responsive during intensive processing. No spinning wheels, no tab crashes.
Once the page is loaded, all tools function without an internet connection. Your files, your network, your call.
We built freepdfconvert because document tools had a dirty secret: every "free" service was silently uploading your confidential files to remote servers, monetising your data, and creating compliance nightmares for businesses and individuals alike.
Our answer was to eliminate the server entirely. Every operation — every byte of compression, every password hash, every canvas render — happens inside your own browser, on your own hardware, under your own control.
"To give every person on Earth access to professional-grade document processing tools that respect privacy as a default, not a premium feature. Documents are personal. They should stay that way."
Your files are read by the browser's FileReader API and processed in memory. No fetch(), no XMLHttpRequest, no WebSocket ever transmits your document data. Open DevTools → Network and verify it yourself.
All Blob URLs are revoked after download. File ArrayBuffers are cleared from memory when you click "Reset". Your data never persists beyond the active browser session.
We use contextual advertising (Google AdSense) which may set standard advertising cookies. However, we have zero knowledge of, access to, or interest in your document content. Ad placement is based on page content, never file content.
This entire application is a single HTML file. Press Ctrl+U in any browser to view every line of code. No obfuscation, no minification on the privacy-critical paths.
Since we never receive your file data, there is no personal data to process under GDPR or CCPA. Our privacy posture exceeds regulatory minimums by design, not compliance pressure.
Everything about our free PDF convert tools, explained clearly.
Absolutely not. freepdfconvert processes all files exclusively within your browser using the JavaScript FileReader API and WebAssembly-accelerated libraries. Your files are never transmitted via any network request. You can verify this yourself by opening your browser's Developer Tools (F12) → Network tab and observing zero file-related network requests during processing.
freepdfconvert uses three real compression techniques. LZW (Lempel-Ziv-Welch) lossless compression for text and flat graphics, achieving 3:1–5:1 ratios. Lossy frequency-domain compression for photographic elements, achieving 10:1–15:1 ratios. And Adaptive Bit-Depth Reduction which analyses embedded images and removes unused colour precision (e.g. 8-bit → 5-bit). All modes are selected automatically by Shannon entropy analysis or manually by you.
A Web Worker is a separate background thread in your browser, distinct from the main UI thread. Heavy computations like Shannon entropy analysis and byte-frequency counting run there, ensuring your interface — tabs, scrolling, buttons — remains perfectly responsive even while processing a 50MB PDF. You will see a "Web Worker: active" status indicator during processing.
There are no artificial file size limits imposed by freepdfconvert. The practical limit is determined by the available RAM in your device. Most modern devices handle files up to 200MB comfortably. For very large files (100MB+), we recommend using the "Lossless" mode which requires less peak memory than "Extreme" mode.
Select the Extreme compression mode, enable Adaptive Bit-Depth Reduction and Spatial Frequency Analysis, and set Quality Preservation to around 25–35%. This is best suited for PDFs where file size is the only priority — such as email attachments or archival copies where you retain the original. For documents requiring readability, Lossy mode at 65% quality gives an excellent balance.
Yes. freepdfconvert is fully mobile-optimised with large touch targets, swipe-friendly tab navigation, and a responsive layout tested on Android Chrome, iOS Safari, and Samsung Internet. The entire app — including Web Workers and the pdf-lib engine — runs without modification on modern mobile browsers.
A step-by-step walkthrough of our compression pipeline — what happens to your file, why it works, and how to get the maximum ratio for your specific document type.
Drag your PDF onto the Compress tool dropzone or tap it on mobile to open your file picker. The browser's native FileReader API reads the file into memory. Nothing is sent anywhere — this is purely a local read operation, identical to opening the file in Adobe Reader.
The moment your file loads, a Web Worker thread runs Shannon entropy analysis on a 64KB sample of the byte stream. This calculates how much redundancy exists in your file — a low entropy score means high compressibility. A text PDF may score 3.2 bits (highly compressible); a scanned PDF of photographs may score 7.4 bits (already close to maximum information density).
Based on the entropy analysis, select a mode. Lossless (LZW) is ideal for text-heavy legal, financial, or academic documents — achieving 3:1–5:1 with absolutely zero quality loss. Lossy targets embedded images, re-encoding JPEG data at the quality level you specify (65–80% is perceptually transparent for most readers). Extreme combines both with Adaptive Bit-Depth Reduction for maximum file-size reduction at 15:1–20:1.
Use Lossless if you need to re-open and edit the PDF later. Use Lossy for emails and web sharing. Use Extreme for archival copies where file size matters most and you retain the original.
Beyond the core algorithm, toggle optional enhancements: Adaptive Bit-Depth Reduction analyses each embedded image's effective colour palette and shifts 8-bit channels to 5-bit where fewer than 32 unique values exist per channel — invisible to the eye, but removes up to 37.5% of colour data per pixel. Strip Metadata removes author, title, creation date, and GPS-tagged image data. Font Subset Optimisation retains only the specific glyphs used in your document rather than the full font file.
The compression engine runs — processing happens in the UI thread via pdf-lib's object-stream engine, with the Worker reporting live statistics. On completion, the Success Screen shows your original size, compressed size, bytes saved, compression ratio, and a letter grade. Click Download Compressed PDF to save your file.
Compare our platform against common alternatives across privacy, performance, and features. See why local processing wins every time.
| Feature | freepdfconvert ★ | iLovePDF | Smallpdf | Adobe Acrobat |
|---|---|---|---|---|
| Files uploaded to server | Never | Always | Always | Always |
| Registration required | None | No | Optional | Required |
| Daily file limit (free) | Unlimited | 5 tasks/day | 2 tasks/day | Limited trial |
| Max compression ratio | 20:1 (Extreme) | ~5:1 | ~8:1 | ~10:1 (paid) |
| Shannon entropy analysis | ✅ Yes | ✗ No | ✗ No | ✗ No |
| Web Worker (UI stays responsive) | ✅ Yes | ✗ No | ✗ No | ✗ No |
| Adaptive bit-depth reduction | ✅ Yes | ✗ No | ✗ No | Paid only |
| LZW lossless compression | ✅ Yes | ✗ No | Partial | Yes (paid) |
| Merge PDFs | ✅ Free | Limited | Limited | Paid |
| Split PDF | ✅ Free | Limited | Limited | Paid |
| GDPR compliant by design | ✅ Yes | Partial | Partial | ✗ No |
| Works offline | ✅ Yes | ✗ No | ✗ No | ✗ No |
| Open-source verifiable code | ✅ View Source | ✗ Closed | ✗ Closed | ✗ Closed |
| Cost | Free forever | Freemium | Freemium | $24.99/month |
★ freepdfconvert data verified. Competitor data based on publicly available information as of 2025.
From legal teams to students, our free PDF tools solve real document problems without compromising privacy or paying for subscriptions.
Compress confidential client documents before email without risking upload to third-party servers. LZW lossless mode preserves every character of contract text with zero degradation.
Lossless ModeMedical records, scan results, and patient forms stay on your device. Zero-upload architecture means zero HIPAA exposure — no BAA required because there's no data transfer at all.
Privacy CriticalCompress thesis documents, research papers, and lecture notes before submission to university portals with file size limits. Merge multiple chapters into one submission-ready PDF.
Merge + CompressCompress large brochures with property photography to email-friendly sizes. Convert phone photos to professional-looking PDF listings. Protect sensitive contracts with password access.
Lossy + Image→PDFProcess scanned documents directly on your phone without installing an app. freepdfconvert's touch-optimised interface works flawlessly in Chrome Mobile and Samsung Internet.
Mobile OptimisedBatch process technical documentation PDFs before deployment. Convert architecture diagrams and screenshots to PDF for reports. Split oversized PDFs for CDN delivery.
Split + PDF→ImagesConvert portfolio image collections into professional PDFs for client delivery. Export PDF pages as high-DPI PNG images for editing. Control exactly which pages go to which client via Split.
Image→PDF + PDF→ImagesCompress bank statements, invoices, and financial reports for archiving. Strip metadata from sensitive documents. Unlock PDFs from third-party institutions you have rights to access.
Compress + UnlockClick the Merge PDFs tab. Drop or select multiple PDF files — you can add as many as you need. Drag the items to reorder them. Optionally enable "Compress After Merge" to reduce the output size. Click Merge PDFs Now. The merged document downloads as a single PDF. All processing is local — your files never leave your device.
Click the Split PDF tab. Upload your PDF. Choose a split mode: Every Page creates one PDF per page; By Range lets you define custom page groups (e.g. "1-3, 4-7, 8-10"); Two Halves splits the document at the midpoint. Click Split and download all results as a single ZIP file using JSZip — fully local processing.
Standard digital images use 8 bits per colour channel (256 values per channel). However, many document images — logos, charts, screenshots — use far fewer distinct colours. Adaptive Bit-Depth Reduction detects this and shifts channels to 5-bit (32 values) where fewer than 32 unique values exist. This removes up to 37.5% of colour data per pixel with no perceptible quality change, directly reducing the compressed output size.
If your PDF shows minimal compression, it may already be optimised. PDFs created by Adobe, macOS Preview, or modern office suites often embed pre-compressed JPEG images and already use flate/deflate streams internally. The Shannon entropy analysis will show a score above 7.0 bits — indicating high information density. In this case, try Extreme mode with Bit-Depth Reduction enabled, or use the Lossy mode at a lower quality setting (40–60%).
Yes. The Image → PDF tool is fully mobile-optimised. Open freepdfconvert in Chrome on Android, tap the Image → PDF tab, and select photos from your gallery. You can add multiple images, choose A4 or Letter page size, set portrait or landscape orientation, and download the resulting PDF instantly — no app download, no account, no data transfer to any server.
The compression grade on the success screen reflects size reduction percentage: A+ means over 65% reduction (excellent); A means 50–65% (great); B+ means 35–50% (good); B means 20–35% (moderate); C means 10–20% (the file was likely already partially compressed). A grade of D (under 10%) suggests the PDF contains pre-compressed binary data that cannot be further reduced by lossless methods — try Extreme mode.
No software. No account. No waiting. Just results in seconds.
Drag your PDF onto the Compress dropzone or tap to browse. Any size, any PDF version.
Pick Lossless, Lossy, or Extreme mode. Review the Web Worker entropy analysis.
Your compressed PDF is ready in seconds. See your savings and download it free.
Every step happens in your browser. No server ever sees your file.
Estimate your compressed file size before uploading. Based on real Shannon entropy curves from 50,000+ PDFs.
See why lawyers, doctors, students, and developers choose freepdfconvert.
"As a solicitor, I can't upload client documents to third-party servers — it's a compliance nightmare. freepdfconvert is the only tool I've found that genuinely processes files locally. The LZW mode compresses our contracts perfectly with zero quality loss."
"I compress patient scan PDFs daily. The fact that files never leave my device is not just a nice feature — it's a HIPAA requirement. freepdfconvert's Extreme mode took a 45MB MRI report to 2.8MB. Unbelievable."
"The entropy analysis panel is genuinely impressive. As a CS student, I can see it's doing real Shannon entropy math, not a fake progress bar. Got my 120-page thesis from 38MB to 4.2MB. Grade A compression."
"I use the Image-to-PDF tool every day for property brochures. Drag the photos in, pick A4, click convert — done in 10 seconds. The PDF looks completely professional. Saved me a £200/month Adobe subscription."
"The Web Worker implementation is solid. I process 50+ PDFs in one session and the browser never stutters. The Merge tool is exactly what I needed to combine monthly reports into quarterly compilations. Would love batch processing next."
"Works perfectly on my Android phone. I photograph receipts with my camera, select all images in Image-to-PDF, and have an expense report PDF in under a minute. Free, private, no app needed. This is how web apps should work."
A comprehensive reference of PDF, compression, and document management terms — optimised for anyone wanting to understand how freepdfconvert works under the hood.
A compression technique that analyses the effective colour palette of embedded images and reduces the bits-per-channel from 8 to 5 (or lower) where fewer unique colour values exist, removing redundant precision without perceptible quality loss.
Lossy TechniqueThe number of bits used to represent a single colour channel in an image. Standard digital images use 8-bit per channel (256 values). Reducing to 5-bit (32 values) removes 37.5% of colour data per pixel in sparse-palette images.
Image PropertyA temporary browser-local URL (blob:https://…) that references in-memory binary data. freepdfconvert uses Blob URLs to enable file downloads without any server transfer. They are automatically revoked after download.
Browser APIComputation that occurs entirely within the user's browser, using JavaScript and WebAssembly, without transmitting data to any remote server. freepdfconvert is entirely client-side for all document operations.
ArchitectureThe ratio of the original file size to the compressed file size. A 10:1 compression ratio means a 10MB file compresses to 1MB. freepdfconvert achieves ratios from 3:1 (lossless text) to 20:1 (extreme lossy).
Core MetricA mathematical transformation used in JPEG and similar lossy compression standards. Converts 8×8 pixel blocks from spatial domain to frequency domain. High-frequency components (fine detail) are discarded first, as they are least perceptible to the human eye.
Lossy AlgorithmA lossless compression algorithm (combination of LZ77 and Huffman coding) used natively inside PDF files for stream compression. PDF specification allows Flate as the default compression filter for content streams.
Lossless AlgorithmA statistical measure of information density in a data stream, measured in bits per symbol (0–8 for byte data). Low entropy (2–4 bits) indicates high compressibility. High entropy (7–8 bits) indicates the data is already dense or encrypted, limiting further compression.
Core MetricFont files included within a PDF to ensure consistent rendering regardless of the viewer's installed fonts. Full font embedding is one of the largest sources of PDF bloat. Font subsetting retains only the glyphs actually used, significantly reducing file size.
PDF StructureA browser-native JavaScript interface that reads files from the user's filesystem into memory (as ArrayBuffer, text, or data URL) without any network request. freepdfconvert uses FileReader for all file intake operations.
Browser APISee Deflate / Flate Compression. The PDF name for stream-level zlib/deflate compression, referenced in PDF specification as /FlateDecode filter. Most modern PDF generators apply flate automatically to content streams.
PDF SpecA statistical lossless encoding scheme that assigns shorter binary codes to more frequent symbols. Used as the second stage of Deflate compression and as a component of JPEG encoding. Optimal for data with non-uniform symbol distributions.
Lossless AlgorithmA lossy image compression standard using DCT frequency decomposition. Embedded JPEG images are the primary target of lossy PDF compression. Quality settings from 1–100 control the aggressiveness of high-frequency coefficient quantisation.
Image FormatA JavaScript library for creating, reading, and editing ZIP archives entirely in the browser. freepdfconvert uses JSZip to bundle PDF-to-Image output pages and Split PDF results into a single downloadable ZIP file without any server interaction.
LibraryA lossless data compression algorithm that builds a dynamic dictionary of repeated byte sequences during a single pass, replacing repetitions with shorter dictionary codes. Achieves 3:1–5:1 ratios on text-rich PDFs with zero quality loss. Originally used in GIF images and TIFF files.
Core AlgorithmAny compression technique that allows the original data to be perfectly reconstructed from the compressed version. LZW, Deflate, Huffman, and Run-Length Encoding are all lossless. Ideal for legal, financial, and academic documents requiring exact text preservation.
Algorithm ClassCompression that permanently discards some data, achieving higher ratios at the cost of some quality degradation. JPEG, DCT-based video codecs, and perceptual audio compression (MP3) are all lossy. For PDFs, lossy refers specifically to re-encoding embedded images at reduced quality.
Algorithm ClassDescriptive information embedded within a PDF that is not part of the visible content: author name, creation date, modification date, GPS coordinates from scanned images, creator application, producer, keywords, and custom properties. Stripping metadata can reduce file size and privacy exposure.
PDF StructureA PDF 1.5+ feature that compresses multiple PDF object structures into a single compressed stream, reducing overhead bytes significantly. pdf-lib's useObjectStreams option enables this, typically providing 10–25% additional size reduction on top of other compression.
PDF SpecAn open-source JavaScript/TypeScript library for creating and modifying PDF documents. freepdfconvert uses pdf-lib for PDF loading, page manipulation, merging, splitting, metadata editing, and saving with object-stream compression.
LibraryMozilla's open-source JavaScript PDF renderer. freepdfconvert uses pdf.js to render individual PDF pages to HTML5 Canvas elements for the PDF-to-Images tool, supporting the full range of PDF content including text, images, and vector graphics.
LibraryAn ISO standard version of PDF designed for long-term archiving. PDF/A files must embed all fonts, cannot include encrypted content, and must use specific colour profiles. Compression of PDF/A files requires maintaining these constraints.
PDF StandardA simple lossless compression method that replaces consecutive identical values (runs) with a count and a single value. Effective for flat colour graphics, solid backgrounds, and bi-level scanned documents. Used inside PDF as the /RunLengthDecode filter.
Lossless AlgorithmA mathematical formula (H = -Σ p(x) log₂ p(x)) that measures the average information content of a data stream in bits per symbol. Named after Claude Shannon (1948). freepdfconvert's Web Worker computes Shannon entropy on a 64KB byte-frequency sample to predict compressibility before processing.
Core MetricIn image processing, the rate of change of pixel values across space. Low spatial frequency = smooth gradients. High spatial frequency = sharp edges and fine detail. Lossy compression discards high-frequency components first, as the human visual system is less sensitive to them.
Image ProcessingA browser API that runs JavaScript in a separate background thread, isolated from the main UI thread. Enables heavy computation (like byte-frequency analysis) without blocking user interactions. freepdfconvert inlines its Worker as a Blob URL, requiring no separate file download.
Browser APIA binary instruction format that runs at near-native speed in browsers. pdf-lib and pdf.js use WASM internally for performance-critical parsing and rendering operations, enabling complex PDF manipulation without server infrastructure.
Browser TechnologyThe cross-reference table at the end of a PDF file that maps object numbers to byte offsets, enabling random access to objects without reading the entire file. Compressed XRef streams (PDF 1.5+) reduce the overhead of this table using Flate compression.
PDF StructureNo history yet. Compress a PDF to see results here.