Pose your own questions and then answering yourself. Impressive.
A few more thoughts on behalf of Adobe:
Adobe Illustrator is not, repeat not, repeat yet again not a general purpose PDF editor. The only PDF files that you can safely edit in Adobe Illustrator are PDF files actually saved out of the same or earlier versions of Adobe Illustrator subject to the following conditions:
(1) The PDF file must have been saved with the Preserve Illustrator Editing Capabilities option enabled!
(2) The PDF file must not have been modified in any way since having been saved from Illustrator. That includes any use of any Acrobat editing tools, annotations, stamps, or anything else!
(3) Any fonts either embedded in the PDF file or referenced but not embedded in the PDF file must be installed on your system and visible to Illustrator. Illustrator does not make use of any fonts actually embedded in the PDF file. (Even in not “subset embedded,” such “fully embedded” fonts contain only the glyph information and some font metrics. Much of the font metric information used by Illustrator is not present in what is embedded in PDF files as fonts!)
Any other PDF files opened in Adobe Illustrator are subject to font substitution, relayout, conversion of type to outlines, improper and unexpected color conversion, and/or content loss. (Adobe Illustrator does not support all aspects of the PDF specification, only those needed to support Illustrator's actual feature set!)
Use of Adobe Illustrator as a routine prepress fixup and validation tool is exceptionally poor PDF workflow practice. You have no idea how many problems reported in these forums and elsewhere end up being traced to “fixing up a PDF file in Illustrator.”
To your original problem, you could easily fixup the stamp in the PDF file to become an integral part of the PDF file itself. Using Acrobat Preflight, use the Single Fixup under Interactive Elements and Properties labeled Flatten all annotations into page contents. That will force any annotations such as stamps and watermarks to become part of the actual PDF pages themselves. This fixup will prompt you for a new file name to save under. The Acrobat Preflight facility has many nifty and useful features that can readily eliminate any need you believe you have to check and fix PDF files in Illustrator!
- Dov