How to Compress a PDF on iPhone

"Attachment too large." Scanned PDFs are mostly images, which makes them heavy — and makes upload limits a constant headache. Compression fixes it in two taps.

The quick answer

Open the PDF in a PDF editor with a compression tool, choose a compression level, and save. Scanned documents routinely shrink by half or more with no visible difference on screen.

Step-by-step: shrink a PDF's file size

1. Open the PDF in Mobile Document Scanner — a scan you made or a file you imported.
2. Choose Compress from the PDF tools.
3. Pick a level. Higher compression means a smaller file; for text documents, even strong compression stays perfectly readable.
4. Save the compressed copy and attach it wherever the original wouldn't fit.

When to compress (and when not to)

Compress for email, web uploads, and messaging — anywhere a size limit bites. Keep the original uncompressed version if the document contains fine print, detailed images, or anything you might need to zoom into later. Best practice: compress a copy, archive the original.

Other ways to cut size

If the file is large because it contains pages you don't need, splitting is smarter than compressing — extract just the relevant pages instead. And if you're combining documents, merge first, then compress once at the end. See merging PDFs on iPhone.