How to Compress a PDF Without Losing Quality
Shrink a bulky scanned PDF down to a size you can actually attach to an email — free, in your browser, with a slider that lets you balance file size against image quality.
What PDF compression actually does
A PDF gets large for one of two reasons: it's full of high-resolution scanned or photographed pages, or it's full of text and vector graphics that are already compact. Compression only helps with the first kind. RedPDF's compressor works by re-encoding each page's embedded images at a lower quality setting — the same trade-off a camera makes when you switch from RAW to JPEG. Pages that are mostly a photograph or a scan can often shrink by 60–90%. Pages that are mostly selectable text barely shrink at all, because there's very little image data to re-encode in the first place.
That's why the tool checks what kind of PDF you've loaded and warns you before compressing a text-heavy document: rasterizing a text page to "compress" it would make the file bigger, not smaller, and you'd lose the ability to select or search the text. Knowing this distinction up front saves you a wasted attempt.
Compressing a PDF, step by step
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1. Open the Compress tab
Go to the Compress tool and drop in the PDF you want to shrink, or click to browse for it.
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2. Pick a compression level
Drag the slider between smaller file size and higher image quality. "Balanced" is a sensible starting point for most scanned documents.
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3. Run the compression
Click Compress PDF. If the file looks text-heavy, you'll see a warning first — you can still continue if you want to.
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4. Compare and download
The result screen shows the before and after size side by side. If you're happy with the trade-off, download the compressed file.
Getting the best result
If your PDF is a batch of scanned pages or photos of documents, start around the "Balanced" setting and nudge it toward smaller file size if you still need to shrink it further — most scanned text stays perfectly legible even at fairly aggressive compression, since legibility depends more on resolution than on JPEG quality. If your PDF is a contract, invoice, or anything exported directly from Word, Google Docs or a similar app, it's almost certainly already small; run it through the tool anyway if you like, but don't expect much change, and consider whether you actually need to compress it at all.
Combining files first? Use the merge tool to build your final document, then compress the merged result once at the end — that avoids compressing the same scanned pages twice and losing more quality than necessary.
Compress PDF — frequently asked questions
Why didn't compression make my file much smaller?
If your PDF is mostly selectable text with few or no embedded images, there's very little to re-encode — the tool will warn you about this before you compress. Compression has the biggest effect on scanned pages and photo-heavy documents.
Will I lose selectable text if I compress a scanned PDF?
A scanned PDF is already just an image of each page with no selectable text underneath, so compression doesn't change that. If your original document does have real, selectable text and you compress anyway despite the warning, that text layer is rasterized and becomes part of a flat image — which is exactly why the warning exists.
Can I undo a compression if I don't like the result?
The tool doesn't overwrite your original file — it produces a new, separate download. Keep the original PDF until you're happy with the compressed version, and you can always re-run compression at a different quality level from the same source file.
Is my file uploaded to compress it?
No. Compression, like every other tool on RedPDF, runs locally in your browser. The PDF is never sent to a server at any point.