How to get a PDF under an upload size limit without making it unreadable
October 9, 2026 · 3 min read
Government sites, insurance claim forms, school portals, broker load boards and HR systems all love a file-size limit — 2 MB, 5 MB, 10 MB. And the PDF you need to upload is almost always just over it. The good news: most oversized PDFs aren't big because of their text. They're big because of a few pictures inside them, and that's fixable.
Why some PDFs are huge
A PDF is a container. Text inside it is tiny: a full page of typed text might take a few kilobytes. Images are what make files large.
- A phone photo is 3,000–4,000 pixels across and often 3–6 MB on its own. Put eight of them into a PDF and you're at 30 MB before anything else.
- A scanned PDF is really a stack of images, one per page, often saved at a much higher resolution than anyone needs to read it.
- Embedded fonts and duplicate images (the same logo stored on every page) add more.
So shrinking a PDF almost always means shrinking the images inside it: lowering their resolution to what a screen or printer actually needs, and compressing them more efficiently.
How small can you go and still read it?
What matters is how many pixels each page ends up with, usually expressed as DPI (dots per inch of the printed page).
| Use | Resolution that's enough | Notes |
|---|---|---|
| Reading on screen, typed text | ~100–150 DPI | Fine for most portals and email |
| Signed forms, small print, receipts | ~150–200 DPI | Keeps signatures and fine print legible |
| Anything someone will print and file | ~200–300 DPI | Above 300 rarely helps for paperwork |
A letter-size page at 150 DPI is about 1,275 × 1,650 pixels — far less than a phone photo, and perfectly readable. That gap is where the savings come from.
Step by step
- Check what the limit actually is, and whether it's per file or per upload. Some portals allow several files of 2 MB each, which can be easier than one huge file.
- Compress with a target in mind. In CrunchFile, upload the PDF and choose a target size (for example 2 MB). It tries progressively stronger compression and stops at the first version that fits, rather than crushing everything.
- Check the result before you upload. Zoom into the smallest text and any signature. If you can read them comfortably, you're done.
- If it's still too big, split it. A 40-page packet might need to go as two files, or the portal might accept the most important pages first.
If the text gets blurry
That means the images were compressed further than the content allows. Try one of these:
- Convert the scan to black and white first. For typed or signed paperwork, black-and-white pages are dramatically smaller than color ones at the same sharpness. Run it through a scan cleanup with a B&W filter, then compress.
- Remove pages that don't need to be there — cover sheets, blank backs of pages, duplicates.
- Compress less and split the file rather than over-compressing one file.
Things compression can't fix
- A photo that was blurry to begin with. Compression won't add detail that wasn't captured. Retake it.
- A password-protected PDF. It may need to be unlocked by whoever created it before any tool can change it.
- A form that must stay fillable. Some compression approaches flatten form fields; if the portal needs the fields intact, compress gently or ask whether a scanned copy is acceptable.
Avoid the problem next time
If you're the one creating the PDF, start small: scan paperwork with a document scanner app instead of attaching raw photos, use black and white for text documents, and don't save at 600 DPI "just in case". A clean 150–200 DPI black-and-white scan of a page is typically a small fraction of the size of the phone photo it came from — and easier to read.