"This file exceeds the maximum attachment size." Every PDF compression search starts with some version of that message. The fix is easy — but if you've ever compressed a PDF and gotten back a blurry mess, you know the real question isn't how to shrink a PDF, it's how to shrink it without wrecking it. Here's what actually works.
What makes a PDF large in the first place
Text in a PDF is tiny — a 100-page novel fits in well under a megabyte. When a PDF is tens of megabytes, the weight is almost always images: scanned pages, embedded photos, or graphics saved at print resolution (300+ DPI) when the file will only ever be viewed on a screen. Compression works by re-encoding those images at a resolution and quality suited to the file's actual use.
Pick the right compression level
The pdfia Compress PDF tool offers three presets. Choosing well is the whole game:
- Light — modest size reduction, best visual fidelity. Use for documents people will read carefully or print: reports, portfolios, anything with fine detail.
- Medium — the sweet spot for email attachments and uploads. Noticeably smaller, still crisp on screens.
- Heavy — maximum shrinkage for when a hard size cap (a 2 MB portal upload, say) matters more than perfection. Fine print may soften; check the preview before sending.
Rule of thumb: start with Medium. If the result is still too big, step down to Heavy; if the document is image-critical, step up to Light and trim size another way (see below).
Three ways to cut size before compressing
- Delete pages you don't need. A 40-page export where you need 6 pages is an 86% "compression" with zero quality loss — use Remove Pagesor Extract Pages.
- Go grayscale for print. If a scan will be printed in black and white anyway,converting it to grayscale can cut image data dramatically.
- Split instead of shrink. When a portal has a per-file cap,splitting the PDF into parts avoids degrading anything.
Do it without uploading
Most compression sites upload your document to their servers to process it — a poor trade for a contract or a medical scan. pdfia's compressor runs entirely in your browser: the file is re-encoded on your own machine and never sent anywhere. It also means there's no size cap on input, no queue, and no watermark on the output.
Frequently asked questions
Why did my "compressed" PDF barely shrink?
It was probably mostly text already, or its images were compressed before. There's a floor below which a document can't shrink without visible damage — if Medium barely moves the number, Heavy won't perform miracles either.
Can compression be undone?
No — re-encoding discards image data permanently. Keep your original file; compress a copy for sending.