Compress PDF Online Free — Reduce File Size, Keep Quality
Reduce your PDF file size without sacrificing readability. Choose your compression level, see the before/after size, and download in seconds.
How PDF Compression Works
PDF files can be large for several reasons: high-resolution embedded images, duplicate font data, verbose metadata, and redundant cross-reference tables. Compression addresses these by re-encoding image data at lower quality, removing unused objects, and restructuring the file for efficiency.
Our compression uses pikepdf, a Python library built on the mature QPDF C++ engine. This is the same technology used by professional PDF workflow tools. It's not a lossy re-render — it works at the object level, which means text and vector graphics are never degraded.
Which Compression Level Should You Choose?
| Level | Typical Size Reduction | Best For |
|---|---|---|
| Low | 10–25% | Documents where quality is critical — legal, medical, print-ready |
| Medium | 25–50% | Most everyday use — reports, presentations, email attachments |
| High | 50–75% | Web uploads, quick sharing where file size matters more than image quality |
A 10MB scanned report compressed at Medium typically comes out at 3–5MB — well within the 25MB Gmail attachment limit and under most university and government portal limits of 10MB.
What Affects Compression Results?
PDFs that compress well contain high-resolution images (photos, scans). PDFs that compress poorly are already optimized, or contain mostly vector text and drawings. A 500KB text-only PDF may only compress to 480KB — the content is simply already efficient. A 15MB scanned document may compress to 3MB.
If you need to combine compression with other operations — for example, merge several PDFs then compress the result — use our PDF Merge tool first, then compress the output.
Frequently Asked Questions
Will compression reduce text sharpness?
No — text and vector graphics in PDFs are stored as mathematical descriptions, not as pixels. Compression only affects raster images (photos, scans). Text remains perfectly sharp at all compression levels.
My PDF didn't get smaller — why?
If the PDF is already optimized (often the case for text-heavy documents or PDFs generated from digital sources rather than scans), compression has little effect. The structure is already efficient. Try the High setting to see if additional savings are possible.
Is compressed output still compatible with all PDF readers?
Yes. The output is a standard PDF file compatible with Adobe Acrobat, Preview (Mac), Chrome's built-in viewer, and any other PDF reader.
Can I compress a password-protected PDF?
No — the password prevents modification. Remove the password first, then compress. If you set the password yourself, open the PDF, enter the password, and save without encryption.
What's the maximum file size I can compress for free?
20MB for free users. This covers the majority of documents — a 20MB scanned report is typically 50–100 pages at 300 DPI. Larger files can be split first using our Split PDF tool.
When Compression Saves the Most — and When It Doesn't
PDF compression works by finding redundancy in the file structure and re-encoding it more efficiently. The results vary dramatically depending on what's in the PDF.
Compresses well (50-80% reduction): Scanned documents where each page is essentially a photograph. A 20-page scanned report at 300 DPI might be 15MB — compression brings it to 3-6MB with no visible quality difference for screen reading.
Compresses moderately (15-40% reduction): Mixed documents with some images and some text. Annual reports, presentations with embedded photos, PDFs exported from Word with embedded charts.
Compresses little (5-15% reduction): Text-only PDFs, PDFs created from digital sources (not scans), PDFs already optimized by Adobe Acrobat. If your PDF is a clean 500KB text document, compression might bring it to 440KB — not worth the effort.
The Three Compression Levels Explained
Low compression removes redundant cross-reference tables, duplicate font data, and unnecessary metadata. Text and images are not touched. Use this for legal or medical documents where image quality must be preserved completely.
Medium compression (recommended for most uses) adds FLATE compression to image streams and removes embedded thumbnails. A typical 10MB scanned document becomes 2.5-4MB. Quality is preserved for screen reading; slight reduction visible if printed at very high DPI.
High compression re-encodes image streams at lower resolution and applies maximum object stream compression. Produces the smallest files but reduces image quality noticeably for high-resolution photography. Acceptable for quick sharing, web uploads, or documents where file size matters more than image detail.
PDF File Size Reference Points
| Document Type | Typical Uncompressed | After Medium Compression |
|---|---|---|
| 1-page text document | 50-100KB | 40-80KB |
| 10-page text report | 200-500KB | 160-400KB |
| 20-page scanned (200 DPI) | 5-8MB | 1.5-3MB |
| 20-page scanned (300 DPI) | 10-15MB | 2.5-5MB |
| 50-page presentation with images | 15-30MB | 5-12MB |
After Compressing — What to Check
Always open the compressed PDF before sending it. Check: text remains sharp and readable, images look acceptable at normal zoom (100%), any form fields or hyperlinks still work. If the result looks degraded, try Medium instead of High compression, or keep the original.
If you need to both merge and compress — for example, combining several scanned pages then reducing the total size — merge first using our PDF merge tool, then compress the combined file.
Compress Before Sending — Attachment Size Limits
Gmail and Outlook both cap attachments at 25MB. Most corporate email servers are stricter — 10MB is common. University portals, government systems, and legal filing platforms often enforce 5-10MB limits. A scanned 30-page contract at 300 DPI typically comes in at 18-22MB uncompressed — over most attachment limits. Medium compression usually brings it to 4-6MB, well within any system's limits.
If you regularly send scanned documents, building a "compress before send" habit saves time and prevents bounced emails. Run the compressed file through our tool first, verify it looks correct, then attach. The whole process takes under 30 seconds.