How can I add a PDF file for an app , where you click on a button to view the file & when you\'re done you get back to screen you were at?
You can also use Quick Look Framework from Apple.
It is very flexible.
You can show your PDF file with zoom feature.
Also you have support for all other types (like png, jpg, docx, txt, rtf, xlsx, zip, mov, etc) of files and it is very easy to use.
Please refer this answer if you want detail description of using QuickLook.framework