Limits

Three cases where smaller is wrong

Compression is a trade. Most of the time the trade is obviously worth it, and these are the times it is not.

Stamps and seals

A round stamp with small lettering is exactly the kind of detail compression smooths away. If the recipient checks it, send the original.

Signatures on a scan

A signature is thin lines, and thin lines suffer first. The signature stays visible but its edges soften, which is enough for someone to question it.

Anything going to print

A printer resolves detail that a screen hides. A file that looked identical on the monitor shows the compression on paper.

What to do instead

Split the document and send the part that is needed, or share the full file another way. Both keep the document intact.