create PDF using SavePict - save changes dialogue

Hi.

I've altered my default image format to PDF as its super fast and makes small files (presumably as it can use vectors if appropriate). I output thousands of binary images in a go so these benefits are a real time saver. A huge annoyance im experiencing is whenever i open the PDF created by igor using ADOBE reader, i always get a "save changes to file" dialogue when i close despite not altering anything. This doesnt happen with other PDF viewers so i can get around the problem but would prefer to use ADOBE reader. I imagine the PDF created by igor is being automaticaaly altered when its loaded in ADOBE reader and altered to fit some current standard. This is probably an issue with ADOBE but thought id ask if ts to do with a problem witht he current PDF creator module used in igor?

Im using windows 7 64 bit, igor pro 6.22a and adobe reader x

cheers
Jonny