What this shows
Page count, the size of the pages (named when it matches a standard paper size), the PDF version, and the document-information fields — title, author, subject, keywords, the application that created it and the software that wrote the file — plus created and modified dates and whether the file is a fillable form.
Why the metadata matters
Those fields travel with the file. A PDF exported from a word processor often carries the author's name, the original file name as the title and the software that made it. If you are about to share a document, check this page first — and use Edit PDF Metadata to change or remove anything you would rather not send.
Password-protected files
A PDF that needs a password to open cannot be read. If the restriction is only on printing or copying, the Unlock PDF tool can remove it first.