Runs in your browser · nothing is uploaded
Compress PDF
Make PDFs smaller without uploading them. Lossless clean-up keeps text as text; the Strong mode turns pages into images for scans and photo-heavy files. You always see the real sizes — and the original if nothing was saved.
How each mode works
Lossless clean-up (keeps text selectable)
- The PDF is parsed with pdf-lib in a background worker.
- Objects nothing refers to — left behind by earlier edits — are dropped.
- Uncompressed streams are Flate-compressed, and Flate streams are re-compressed at the highest level. Both are lossless.
- Optionally: title/author, XMP metadata, embedded page thumbnails and editor private data are removed.
- Optionally: plain RGB JPEG photos are re-encoded at your quality and maximum size — kept only if at least 5% smaller.
- The file is saved with compressed object streams, re-opened to check it has the same number of pages, and compared with your original.
Strong (pages become images — text no longer selectable or searchable)
Each page is drawn with PDF.js at the DPI you choose (one page at a time, to limit memory), saved as a JPEG, and placed on a page of exactly the original size in a new PDF. Very large pages are capped at 25 megapixels.
Worked example
A scanned 20-page A4 document at 100 dpi becomes twenty 827 × 1,169 pixel JPEGs. If the new file is smaller you get it with the percentage saved; if it isn't (common for text-only PDFs), you're told “No saving” and offered the original.
Strong mode: pixels per page
PDF page sizes are measured in points (1/72 inch), so pixels = points × DPI ÷ 72. Calculated when this page was built, by the same code the tool runs.
| DPI | A4 page (pixels) | US Letter page (pixels) |
|---|---|---|
| 72 | 595 × 842 (0.5 MP) | 612 × 792 (0.5 MP) |
| 100 | 827 × 1,169 (1 MP) | 850 × 1,100 (0.9 MP) |
| 150 | 1,240 × 1,754 (2.2 MP) | 1,275 × 1,650 (2.1 MP) |
A4 is 210 × 297 mm (ISO 216); US Letter is 8.5 × 11 in; a PDF point is 1/72 inch (ISO 32000). Checked 2026-10-07.
Limitations, plainly
- Savings vary a lot. Text-only PDFs from modern apps often shrink by little or nothing in Lossless mode. Big gains come from scans and photos.
- Photo shrinking only touches plain RGB JPEGs. CMYK, greyscale, masked, PNG-style (Flate) and JPEG 2000 images are left as they are.
- Forms and annotations: Lossless mode keeps form fields, links and comments. Strong mode flattens their current appearance into the picture — fields can no longer be filled and links don't work.
- Encrypted PDFs can't be processed, and digital signatures are invalidated by any change.
- Large files (up to 200 MB each, 20 at a time) are processed in memory; Strong mode on hundreds of pages can take a while. You can stop at any time.
Frequently asked questions
How do I reduce the size of a PDF?+
Add the PDF, pick a mode and press Compress. Start with Lossless clean-up — it keeps text selectable. If the file is mostly scans or photos and still too big, turn on “Also shrink JPEG photos”, or use Strong mode, which turns each page into a JPEG.
Why didn't my PDF get smaller?+
Many PDFs are already compact — for example ones exported by modern word processors. Re-saving can't remove what the file needs. When the result isn't smaller, the tool says so, shows the real sizes and offers your original instead of a bigger file.
Will compressing a PDF make the text blurry?+
Not in Lossless clean-up: text, vector drawings and fonts are not changed. Photo shrinking only re-encodes JPEG photos. Strong mode does turn text into pixels — at 72 dpi small print can blur, at 150 dpi it usually stays readable.
What is the difference between the two modes?+
Lossless clean-up rebuilds the file more compactly (object streams, maximum Flate compression, unused objects and optionally metadata removed); the content is the same. Strong mode renders every page as an image and builds a new PDF from those images: often much smaller for scans, but text is no longer selectable or searchable and links and form fields are lost.
Which DPI should I use in Strong mode?+
72 dpi is smallest and fine for reading on screen. 100 dpi is a sensible middle ground. 150 dpi keeps small print readable when printed. An A4 page at 150 dpi is 1,240 × 1,754 pixels.
Can I compress a password-protected PDF?+
No. Encrypted PDFs can't be opened here — remove the password in a PDF app you trust first. A digitally signed PDF can be compressed, but the signature will no longer be valid.
Is my PDF uploaded?+
No. Lossless clean-up runs in a background worker in your browser, and Strong mode draws pages with PDF.js on your device. The file never leaves your computer or phone.