You can do this using ED File Explorer. Navigate to the file you want and long press on it. Select "More" and you should have an option to add it as a desktop shortcut. Don't know if there's a way to do it without ED File Explorers.
What app do you use for PDF files? On my various devices I use Documents to Go, PDF Viewer and Office Suite Pro. None of these offer a "Save to Homepage" option when a file is long-pressed, at least not in the versions that I have.
Then long press on a home screen where you want the shortcut. the screen will flip up and 'Shortcut' will be the option on the lower right. Tap Astro, then it will allow you to select a file you want to make an icon for on a homescreen.