No need to convert, the pdf will work as is sa iPhone.
I have tried a few 'free' pdf readers from the app store but have not been satisfied with them. Some of them are not able to open large files or crashes in the middle of a doc. Finally settled for the 99cent GoodReader app. Have not had any problems with it.
Loading of file can be done via wifi connection. Usually, merong button sa iPhone app which will give you the http address to connect to para maka-transfer ng file.
Etong link sa Goodreader, may mga "How to's" dito...