You basically need to start by finding out the format of the file, which is not an easy task if it is a "closed" format (I once had to attempt to decode an Excel file, and gave up after a couple of weeks!).

There may be information around that you can use, one place to look is www.Wotsit.org , as they have detailed descriptions of many file formats.

Alternatively, you may be able to use a method such as Automation (if the application supports it).