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About this tool
A closer look at Compress PDF
Compress PDF reduces file size in two ways: lossless structural optimization that tightens the internal PDF object streams, and re-encoding of large embedded JPEG images at a lower, quality-controlled level. Text, vector graphics, fonts and form fields are preserved and remain selectable.
Large PDFs are almost always large because of the images inside them — scanned pages, high-resolution photos and pasted screenshots. For those files, re-encoding the big JPEG images at a sensible quality gives the biggest reduction. Text-only PDFs have little to compress and benefit mainly from the structural pass.
You can pick a preset (low, balanced or strong) or a custom mode with an image-quality slider, and the tool shows an estimated size before you commit. Processing happens in your browser and the smaller file is downloaded locally. Because compression is one-way, keep a backup of the original before you start.
Supported files
How to use it
- 1Choose a PDF
- 2Process locally
- 3Download the optimized copy
What you can use it for
- Shrinking a PDF so it fits under email attachment limits.
- Reducing file size before uploading to portals with size caps.
- Freeing space when archiving many PDFs locally.
- Sending a large report to a colleague on a slow connection.
- Preparing exported presentations or brochures for fast sharing.
What to keep in mind
- Already-optimized PDFs may shrink very little.
- Only JPEG-encoded (DCTDecode) images are recompressed; PNG, TIFF, JPEG 2000 and raw bitmaps are left untouched.
- Small images (icons and logos) are skipped because recompressing them adds artifacts for little gain.
- Image-heavy PDFs see the biggest gains; text-only PDFs see modest ones.
- Compression is not a substitute for re-exporting a better-quality original.
- Very large PDFs (above 100 MB) are processed in browser memory and may be slow on low-memory devices.
Troubleshooting
The file barely changed
Check whether the PDF is already optimized or mostly text. If it is image-heavy but compressible only via PNG/TIFF images, compression will have limited effect because the engine deliberately leaves non-JPEG images untouched.
Compression looks slow on a large file
Image re-encoding is the slowest step and runs on your device. Wait for the progress screen — memory-heavy jobs may take a minute or two on large documents.
Text looks softer after strong compression
Strong mode resizes large JPEG images more aggressively. Re-run with balanced or custom quality instead — text itself is never re-rendered, so the change comes from image quality.
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Frequently asked questions
Is compression lossless?
Structural compression is lossless. Large embedded JPEG images may be re-encoded at a quality-controlled level; all text, vectors and fonts are preserved.
Why isn't my file getting much smaller?
Already-optimized PDFs shrink very little, and only JPEG-encoded images are recompressed — so text-only files see modest gains and image-heavy files see the biggest.
Which preset should I use?
Start with balanced for a good quality/size trade-off. Use low to stay closest to the original, or strong when you need the smallest possible output and are willing to accept slightly softer images.
Can I restore the original after compressing?
No. Compression produces a new file and the change is one-way — keep a backup of the original before you compress.
Does compression keep text selectable?
Yes. Only large JPEG images may be re-encoded; text, vectors and fonts are preserved exactly.
Will a 100-page scanned document compress well?
Usually yes, because scans contain large JPEG images. If the result is still large, consider splitting the document into logical sections instead of sending one huge file.