I think there are two good options
- Modify the Convert task to also support additional file types
- Create an EPDM addin
In both cases the process is rather similar
- Determine what program shall be used to convert the document (look at the extension)
- Connect to the program, use its API to open, save and then close the file.
One last point if working with Office documents. If you are using Office 2007 or higher use the program's SaveAs pdf function rather than printing to a pdf print driver. The output seems more reliable.