A PDF must be put into an external program after being exported to be edited, you can't make direct changes to it. This eliminates answer choice A.
You can print documents with other extensions besides .pdf, such as those of Word documents and such, it doesn't have to be a .pdf. This eliminates answer choice B.
Since you can't directly edit a PDF, C is a possible answer.
Files don't have to be saved as a .pdf, especially just for the first time. Whenever you save a file, first time or not, you can save it as anything, and there's no reason to have to save it as a .pdf. This eliminates answer choice D.
So the answer is C. it contains material you don't want changed.
