Compress PDF guides

Almost nobody wants to compress a PDF for its own sake. They want to get past a limit: a 25MB email attachment cap, a government upload form that refuses anything over 2MB, a portal that silently fails at 5MB. So these guides are organized around targets rather than around settings, and they say what compression actually costs, which is usually image detail on scanned pages. Text-based PDFs compress differently from scans, and knowing which one you have saves a lot of guessing. The main guide covers the common case of getting under a size limit for email. The specific guides handle the awkward targets people are actually given, and the explainer covers what is really happening to your file when it shrinks, so you can judge whether the result is good enough before you send it. Where a PDF genuinely cannot reach the target without becoming unreadable, the guides say that too, and suggest what to do instead.