What are you wanting to do with the file?
You could store a .PDF document in the IFS or as a binary large object in a data file, but it seems to me that because a .PDF is an image file, a character based emulator wouldn't be able to interpret it. But you can open other file types, such as a .TXT or .CSV, from the i, in many different ways.
Otherwise, you'd need an application capable of reading and displaying a .PDF, and I don't know whether there is such software available for IBM i (fomerly OS/400). Otherwise, you'd have to create something, which is no small undertaking. And since Adobe already exists and is widely available, why would you need to?