when encoding a pdf using characters from a foreign alphabet (e.g. Cyrillic), it is not possible to open the document with acrobat reader. (This only relates to an encoding with security settings earlier than acrobat 9).
The PDF Reference (version 1.7, algorithm 3.2) says: "The password string is generated from OS codepage characters by first converting the string to PDFDocEncoding. If the input is Unicode, first convert to a codepage encoding, and then to PDFDocEncoding for backward compatibility."
After some digging, I figured out that PDF-XChange Viewer is using an ASCII codepage (i.e. replacing all foreign characters with an question mark character '?'). Hence I can open the document in acrobat reader or PDF-XChange Viewer typing the correct amount of questions marks. Not very secure is it?
Adobe Acrobat on the other hand uses the windows 1251 (on windows) and ISO 8859-5 (on unix) codepages. So basically adobe is not compatible on different platforms, but at least the password is secure.
Anyhow, PDF-XChange Viewer is not at all compatible with Adobe.
By the way: If you use acrobat 9 and later (which corresponds to revision 5, AES 256), the password is encoded in unicode. Just use this setting and your pdf is secure and compatible (if you use a strong password
.Greets,
Andi
