Pick a level, then look at the output size before sending anything.
Check the smallest text and any stamp. If they survive, the file is safe to send.
Two 60MB files send where one 120MB file will not.
Sending a file in a WeChat chat caps out around 100MB per file; mail attachments usually stop at 20-25MB once encoding overhead is counted. Both limits apply to the finished file, so renaming or zipping a 130MB scan achieves nothing. Knowing which wall you are against decides what to do: a chat limit is usually worth compressing for, a 20MB mail limit often is not.
Open the file and check whether the pages are photographs. Forty pages of text weighing 80MB is almost certainly a stack of phone photos pasted in; the same content rescanned at 200dpi lands near 5MB. Compressing a photo-heavy PDF works well. Compressing one that is already mostly text changes almost nothing, because there is nothing to throw away.
A proper compressor re-encodes the embedded images and leaves text and vector lines untouched, so the contract body stays sharp while the photos behind it soften. The visible cost shows up on scans: thin handwriting and faint stamps blur first. For a signed document, compress once, look at the signature at 100%, then decide.
If the result is still over the limit, splitting into two files is faster than chasing another ten percent: send pages 1-20, then 21-40, or replace the attachment with a share link. And for government or school upload forms, read the stated cap first, because those usually reject at 2MB or 5MB and no compressor gets a colour scan under 2MB without destroying it.
Pages, text and links stay. Embedded images are resampled, which is where the size comes from.
Yes. It runs in the browser, so a phone browser works and the file is never uploaded.
On screen, barely. Printed at A4, a heavily compressed scan looks soft but stays readable.