Compress PDF

How PDF Compression Works

Every time you compress, the tool runs both of the following and keeps whichever produced the smaller file. You never choose between them — the winner is decided by measurement, and the result message names the one that won.

• Lossless re-save — the document is reopened and written out again with its objects packed into compressed object streams. Anything the file no longer references is dropped along the way. Text stays text, links stay clickable, and the page is byte-for-byte visually identical.
• Image-based re-render — each page is drawn onto a canvas at your chosen DPI, encoded as a JPEG at your chosen quality, and placed into a new document as a single full-page image at the original page dimensions.

The trade-off nobody mentions

Image-based compression does not re-compress the pictures inside your PDF. It photographs the entire page. Everything that made the file a document rather than a picture is gone from the output: no selectable text, no search, no copy-paste, no screen-reader access, no working links. We measured it — a text page that reported 14,586 characters before came back with exactly zero.

This is why the smaller-of-the-two rule matters more than it looks. For a text document the JPEG route is not slightly worse, it is catastrophically worse: our six-page text sample was 7 KB losslessly and 1.6 MB as JPEG at 150 DPI — over two hundred times bigger. It loses by such a margin that a text document is never silently flattened. The protection is automatic, not a setting you have to remember.

Scanned pages invert the picture completely. There is no text to lose, and the page is already an image, so re-encoding is exactly the right move — our image-heavy sample dropped from 5.8 MB to 3.5 MB, a 39% saving.

Quality and DPI

Both settings only affect the image-based attempt; they have no effect at all if the lossless result wins. Quality is the JPEG quality factor, and DPI controls how many pixels each page is rendered at — 150 DPI doubles the linear resolution of the 72 DPI baseline, so it produces roughly four times the pixels.

• 80-95% — Minimal quality loss. Best for documents with fine text or detailed graphics
• 60-80% — Good balance. Suitable for most documents, reports, and presentations
• 30-60% — Aggressive compression. Good for scanned documents and image-heavy files

DPI is clamped between 72 and 300 and defaults to 150. Values outside that range are pulled back to the nearest end rather than rejected.

Tips for Best Results

• Scanned documents and PDFs built from photographs see by far the largest reduction
• A text-only PDF is already compact — expect little or nothing, and that is the correct outcome
• Use 150 DPI for a good balance between quality and file size
• Use 72 DPI for maximum compression when screen viewing is the only use case
• Read the result message. It tells you which strategy won, which is how you know whether your text survived

Limitations

• Hard limit of 100 MB. Larger files are refused outright rather than attempted, because rendering every page to a canvas is memory-hungry.
• Sometimes the answer is no. If neither strategy beats the original, the tool reports "No reduction" and deliberately does not download anything — handing back a file that grew would be worse than useless. On an already-optimised PDF the lossless pass can come out a couple of bytes larger.
• Image-based output loses the text layer, along with links, form fields and bookmarks. The tool shows which method was used after compressing.
• All processing happens in your browser — very large PDFs (50+ pages) may take longer depending on your device.
• Password-protected PDFs cannot be opened and will report an error.