How to compress a PDF without making it look terrible

You attach the file, and the mail client refuses it. The usual instinct is to compress hard and hope. A better approach starts with knowing what is heavy in the first place.

What makes a PDF big

Text is tiny. A hundred pages of pure text is often well under a megabyte. Weight comes from images: scanned pages, screenshots at retina resolution, and photographs embedded at print quality in a document that will only ever be read on a screen. Embedded fonts and duplicated assets add a little more.

What compression does

Compression mostly downsamples those images and re-encodes them more aggressively. Text and vector graphics stay sharp because they are described mathematically, not as pixels. That is why a text-heavy report compresses beautifully and a photo book barely moves.

Getting under a limit

1. Compress once at a moderate level and check the size. Very often that is enough.
2. If it is still too large, look for pages that do not need to be there — appendices and duplicated covers are common.
3. Split the document and send it in two parts rather than compressing until the scans are unreadable.
4. For a document destined for print, keep the original and send the compressed copy only by email.

Keep the original

Compression is lossy: the detail thrown out does not come back. Always keep the uncompressed file, and treat the compressed one as a copy made for a specific purpose.