If you previously used Accpac Plus, then AR# files are the statement spec files used there. You can use Adagio Receivables to convert these to a format usable by Adagio:

Open the Statement designer program.
From the File menu, choose Open.
In the Files of Type drop-down field, choose 'Dos spec AR#*.*'
You will see your DOS specs listed. Pick one and choose to Open.

The specification is then converted, and the original AR# file is left unchanged. It is not deleted. You can then save the converted specification.