Questions about PDF in general

When posting a question on StackOverflow, people can tag their posts as iText or iTextSharp questions. This allows me to quickly find those questions by performing a simple query for posts tagged as itext* questions. This includes the tags itext, itextsharp, itextpdf and itextg.

However, not all questions tagged this way are iText-related. Sometimes, people using iText have questions that are about PDF in general.

Can I change the page count by changing internal metadata?

Does a PDF file have styles, headers and footers?

How do I rotate a PDF page to an arbitrary angle?

How should I interpret the coordinates of a rectangle in PDF?

How to allow page extraction when setting password security?

How to close a PDF file to recreate it? (File in use problem)

How to disable the save button and hide the menu bar in Adobe Reader?

How to encrypt PDF using a certificate?

How to extract a page number from a PDF file?

How to find out if a PDF file compressed or not?

How to get the page number of an arbitrary PDF object?

How to hide the Adobe floating toolbar when showing a PDF in browser?

How to protect a PDF with a username and password?

How to protect an already existing PDF with a password?

What does "Not LTV-enabled" mean?

What is the connection between LTV and document timestamps?

What is the difference between iText, JasperReports and Adobe LC?

What is the size limit of pdf file?

Where is the origin (x,y) of a PDF page?

Why are PDF files different even if the content is the same?

Why do PDFs change when processing them?