Adobe no longer sells CS1. It is considered "abandonware" by many collectors. You cannot buy a digital download from Adobe. However, there are a few legitimate avenues:
One of the more unique—and controversial—aspects of CS1 was its . The software was programmed to detect scanned images of various banknotes; if a user tried to open or print currency, the program would refuse the command. System Requirements for CS1 adobe photoshop cs1