Longer pieces on the problems these tools exist to solve, and on the ones they cannot. Each one is written for someone trying to get a specific job done, and each is honest about where a browser tool stops being the right answer.
Why your PDF is large, which fix applies to your file, and what to do when compression will not help.
Read How to get a PDF under an email attachment limit
Size, contrast, quiet zones, error correction and logos — the five things that decide whether a printed code works.
Read Why printed QR codes fail, and how to make ones that do not
The mechanics of server-side file tools, what their privacy policies actually commit to, and when it matters.
Read What happens to your file when you upload it to a free tool
Why a scanned PDF cannot be searched, why it is large, and what redaction really requires.
Read Working with scanned documents: what a scan is and is not