Serial Numbers

I'm sure it is possible, but I am unsure how to do this. I have created a Sale coupon that I was going to put up on a site that I manage, for visitors to print out and bring to the store. The coupon is currently a .png, however I was planning on converting to a pdf. I would like to put on the coupon a serial number that increases by 1 everytime the page is viewed. I dont really care if someone refreshes the page and skews the numbers. Is this possible and could someone give me some help? Thanks Gary __________ Information from ESET Smart Security, version of virus signature database 5273 (20100712) __________ The message was checked by ESET Smart Security. http://www.eset.com