Hi Topics9,
I checked your account and i found that you have subscribed for Acrobat Pro XI on 25 Dec 2014.
Using Acrobat XI you should be able to edit PDF. However if the pdf document is protected then it cant be possible.
I wasnt able to find any other details of previous purchases. And i am not sure what was previously installed on your machine using which you were able to edit PDF files.
You may contact your IT they may have installed Acrobat using University/School license.
Regards,
Ajlan Huda.