I use an application called air sharing. available in the itunes store. syncs files on your computer with your iphone / ipod touch. getting the file onto the phone isnt as much of a problem as actually viewing the pdf if its to big. there isnt enough memory on the iphone / ipod touch to open huge files. a 20 meg pdf you should be ok but i wouldnt go much larger then that or it will lock up your phone for 10 minutes and then simply crash the os.