iText can tell you more about a PDF. What is the size of a page? Which measurement unit is used. All of these questions can be answered with a simple example using PdfReader.
How To find internal links in a PDF file?
How can I find the border color of a field? | iText 5 PDF Development Guide
How can I read Roman page numbers? | iText 5 PDF Development Guide
How do I get an object if I have its indirect reference?
How to extract embedded streams? | iText 5 PDF Development Guide
How to get the UserUnit from a PDF file? | iText 5 PDF Development Guide
How to get the author of a "free text" annotation?
How to get the page width and height of a PDF document?
How to read PDFs created with an unknown random owner password?
How to read bookmark titles? | iText 5 PDF Development Guide
Why do I get an "InvalidPdfException: PDF header signature not found"?
Why is the page size of a PDF always the same, no matter if it's landscape or portrait?