I have a problem with digital signatures in Adobe Reader.  I have Adobe Acrobat 9.  I am including a form with multiple signature fields in a pdf portfolio.  This portfolio is circulated to collect signatures from users in different departments, some have Acrobat and some have Reader only.  I make sure that features have been extended for Reader. Most of the time they are okay.  But every once in a while (at least once or twice per week) I get a user telling me they can't sign.  No message or error of any kind, just a quick blink but no signature.  As a work-around I've had to save a copy and re-extend features.  This can be time consuming when there are a few documents I need to circulate.  Please help.