Adobe Acrobat cannot create a PDF

Greetings,
I have a question concerning the editing of PDF files. I have a class project that I wanted to edit some few things but it is in form of PDF. So I installed Adobe Acrobat, problem is whenever I try to open the document I get an error as shown below. Can anyone help?

Adobe Acrobat
There was an error opening this document. The file is damaged and could not be repaired.
