Guides
Practical guides
Short, specific write-ups about doing these jobs well — written by the people who run the tools.
Compressing a scanned PDF without making it unreadable
Scanned documents are images in a wrapper — that changes which settings matter.
Merging and splitting: how to avoid the classic mistakes
Page order, bookmarks and file size — the three things that go wrong.
Password-protecting a PDF (and what unlocking can and cannot do)
What the password actually protects, and the difference between user and owner passwords.