Why compress a PDF?
PDFs grow large faster than almost any other everyday document format. A handful of scanned pages, a portfolio full of renders, or a deck built from high-resolution exports can easily reach tens of megabytes — enough to bounce off an email limit, stall on a slow connection, or get rejected by an upload form with a hard cap.
Compression solves that, and it's worth understanding what it actually does before you rely on it, because this method involves a specific and permanent trade-off.
How this tool works
This compressor renders each page of your PDF to an image at a reduced scale and quality, then rebuilds a new, smaller PDF from those page images. It uses open-source libraries — pdf.js to read the original and jsPDF to reassemble the output — running entirely inside your browser tab. No file is uploaded anywhere, which matters a great deal given that the documents needing compression are so often contracts, client decks, and confidential paperwork.
It also means there's no upload wait. When you're compressing something twenty minutes before a meeting, that's usually the slowest part of using a conventional web service.
The trade-off, stated plainly
Because each page becomes an image, text in the compressed PDF is no longer selectable, searchable, or copyable. Screen readers won't be able to read it either. The document still looks correct and prints correctly — it simply is no longer text, it's a picture of text.
For a scanned document, this costs you nothing you had; a scan was already an image. For a visual portfolio or a design deck, it's usually irrelevant. For a contract someone needs to search, a report that will be quoted from, or any document with accessibility obligations, it's a real loss. In those cases, keep the original and send that instead, or reduce size at the export stage rather than compressing the finished PDF.
Always keep your original. This process is not reversible — the discarded resolution is genuinely gone, and re-saving at a higher setting won't bring it back.
Choosing a level
Low applies light compression and keeps text and images comparatively crisp — the right choice for portfolios, design work, and anything where visual quality is being judged. Medium balances size against quality and handles the common case of getting a deck under an email limit. High delivers maximum size reduction with visible softening; use it for records and archival scans, but avoid it for drawings with fine linework or small dimension text, where the detail carries meaning.
Under time pressure, start at Medium, check the result on your most image-heavy page, and adjust once. Two attempts almost always lands it.
When compression isn't the right answer
If the file still won't fit after Medium compression, resist the urge to push to High and hope. A 40-page drawing set squeezed under 5 MB is usually illegible, and sending something unreadable is worse than sending two emails.
Better options at that point: split the document and send it in parts, or send a link to cloud storage instead of an attachment. Also aim comfortably below any hard limit rather than exactly at it — mail systems add encoding overhead in transit that can inflate an attachment by roughly a third, so a 9.8 MB file may still bounce off a 10 MB cap.
Preventing the problem at export
The most effective fix happens before the PDF exists. If you still have the source file, exporting at screen resolution rather than print resolution produces a far better-looking document at a given size than compressing a print-resolution export afterwards. Most design and office applications offer a "smallest file size", "web", or "screen" preset that does exactly this.
For scanning, use greyscale or black and white at 200–300 DPI rather than full colour at 600. For ordinary paperwork this alone can cut file size by an order of magnitude with no meaningful loss.
For a fuller walkthrough of these decisions, see our guide on shrinking a PDF without wrecking it.