iPhone save PDF file and view it I have a PDF file on my Mac and I want to copy it into my iPhone and then read it.
How can I do that?  

I already tried to plug the iPhone cable into my Mac, but it seems Finder doesn't let me save a file onto it. Before I had an iPhone, I used a Windows phone and could simply transfer my file to the phone and view it.

Do I need additional software? I have an iPhone 4S running iOS 5.1.
You need to use iTunes to transfer it to the app on your iPhone that will take ownership of it. The simplest solution is to use iBooks, which you can find in the App Store on your iPhone if you haven't downloaded it already:


Drag the PDF into iTunes
Select your device on in the left hand pane, then select "Books" on the top. 
Make sure "Sync Books" is checked, and if you're syncing selected books, check the check box by the PDF you just added.
Hit Apply


The PDF should now be in iBooks on your iPhone.