Transfer PDFs from your Computer
Read PDFs that were on your computer on your iPhone for convenience when you are not in front of your computer.
Install the iBooks app on your iPhone. Get it for free from the App Store here.
Should this not be listed in the Library, edit your Preferences in the main iTunes menu to make sure Books are selected.
Check to see if the PDF is viewable via a file browser such as Finder on Mac or Explorer on Windows. It should appear as an icon on the desktop. You need to be able to see the PDF you want to move to your iPhone as well as iTunes at the same time.
Drag and drop the PDF to the iTunes Book library. The PDF should appear in both places.
After plugging your iPhone into your computer, select it in the Devices menu on iTunes.
Click on the Books tab. You'll find "Books" in the bar across the top of the main frame per below.
Check the Sync Books checkbox which will sync all books or sync selected books.
You are now synced!