The only way to convert .adp files from Microsoft Access to .accdp files, would be to use some of the later versions of Access that does support .accdp files. No other program can probably help you with this conversion, as MS Access formats are proprietary and not well supported in 3rd party software.
When you open your .adp files in MS Access, you can simply use File ► Save as.. function to re-save your databases to ACCDP format.