PDF files come in all shapes and sizes. They vary from relatively simple to mind-numbingly complex. PDFs can also differ in their degree of conformance to the PDF specification -- the bad ones are often called malformed PDFs.
Sometime ago, Adobe made the decision to automatically repair these malformed PDF files in Adobe Reader and Adobe Acrobat when they encountered them in the wild. Usually, users don't even know that a PDF has been repaired. It happens silently in the background as the PDF is opened. Often, the only clue that the PDF has been repaired is that the Save button is enabled.
Arguably, automatically repairing these malformed PDF files is a good thing. The average user is not going to know what to do if they are told that their PDF file has syntax issues and cannot be opened. They do not care; they just want to view their PDF.
On the flip side, it is also effectively rewarding the bad behavior of the offending PDF producer that has produced the malformed PDF. The PDF producer does not have to worry about creating a PDF that conforms 100% with the PDF specification because it knows that Adobe Reader will automatically repair it.
What is more, the fact that Adobe automatically repairs these PDF files means that other PDF applications also have to automatically repair PDF files because Adobe products are the benchmark for processing PDFs.
Many times when a 3rd party PDF vendors point out to the user that the reason that a particular PDF fails to process correctly in their product is that it is a malformed PDF. To which the user usually replies, "But it opens in Adobe Reader." Well, yes, that is true, but should it be?
It is a tough situation, but perhaps Adobe can take the middle way: automatically repair the PDF file but alert the user to the fact that the PDF is malformed. The user can then take this information and report the error to the PDF vendor who produced the malformed PDF file.
This approach would both cover all bases and reduce the chances of malformed PDF files proliferating.
OK, so you want to stamp your document. Maybe you need to give reviewers some advice about the document's status or sensitivity. This tip from author Ted Padova demonstrates how to add stamps with the Stamp Tool along with related comments.