The program I use for music composing is MidiNotate Composer (http://www.notation.com/NotationComposer.htm
). I don't do a great deal of composing, but on the occasions when I've needed to use the program it has worked fairly well. Several of my more computer-savvy musical friends use Noteworthy Composer (http://www.noteworthysoftware.com/composer/
) and speak very highly of it, but I have no experience with that software so I'm not sure if they're telling the truth or lying through their teeth.
In MidiNotate Composer you can select the option of composing for just piano, and I think you have that choice in Noteworthy Composer as well. I do not know if these programs have PDF-saving capabilities or not.
Disclaimer: the statements above have been written by a technologically challenged individual and have not been evaluated by a more knowledgeable person. Proceed at your own risk.