What Compress PDF does
Compress PDF shrinks a PDF's file size by rendering each page as a compressed image and rebuilding the document from those images, entirely in your browser. It's aimed at the files that benefit most from this: PDFs made of scanned pages, screenshots, or photos, where most of the file size is image data rather than text.
How this works - and what it costs
There is no way to run a general-purpose PDF compression algorithm entirely client-side the way a dedicated desktop tool can. Instead, this tool takes the one approach that reliably works in a browser: it renders every page to a canvas, re-encodes that as a JPEG at the quality level you choose, and places the result into a new PDF at the same physical page size. That genuinely shrinks image-heavy and scanned PDFs, often considerably - but the output is image-based, so any selectable or searchable text in the original becomes a picture of text and can no longer be selected, searched or copied. For a PDF that's already mostly plain text with little image content, this approach may not shrink the file much, and can occasionally make it larger - which is exactly why the result is compared against the original size before you download it.
Choosing a compression level
- High quality - renders at a higher resolution and lighter JPEG compression. Smaller size reduction, but pages stay sharp even when zoomed in.
- Balanced - a reasonable middle ground for most scanned documents and photo-heavy PDFs.
- Maximum compression - the smallest resulting file, at a noticeably softer, lower-resolution result best suited to documents that will only ever be viewed on screen at normal zoom.
When to use a different tool instead
If the PDF's text needs to stay selectable and searchable after compressing, this tool is the wrong fit - flattening to images removes that regardless of quality level. A desktop PDF editor with genuine content compression (recompressing embedded images without rasterizing the whole page) will do better for text-heavy documents that still need some size reduction.
Common uses
- Scanned documents — shrinking a phone-scanned or flatbed-scanned PDF before emailing it.
- Photo-heavy reports — reducing a file built mostly from embedded images or screenshots.
- Upload size limits — getting a file under a form or email attachment size cap.