Can I transfer a PDF to iPhone then use gmail to send it by email?
The commercial answer is to install a good quality PDF viewer. Even better would be to install GoodReader which started out as a PDF handler but can now handle a number of different file types and do any number of things with them, including email.

http://www.goodiware.com/goodreader.html

https://itunes.apple.com/us/app/goodreader-for-iphone/id306277111?mt=8&amp;ign-mpt=uo%3D4