I have found that Many users have confusion about PDF and PDF/A or otehr versions. However I am going to explain here basically difference between PDF and PDF/A.

PDF/A is a special type of PDF. Opposite to Simple PDF, the PDF/A ISO standard is described for long-term archiving. Especially, PDF/A indicates a ‘profile’ for electronic documents that makes sure that the documents can be reproduced in future. It provides us a method for representing electronic documents in a way that conserves their visual appearance over time, independent of the programs and systems used for creation, storage or editing the documents.