Convert .ADF Files back to my old amiga 500

[Piru]

No, not without special hardware.

If you manage to transfer the adf to your amiga (via serial, ethernet, IDE hd, CrossDOS or whatever), you can write them to floppy on the amiga itself.

[Piru]

and the program that converts .adf files back into disks is an Amgia program, though PC versions are theoreticaly possible.

This is not a problem, if the disk writing works (Catweasel for example), you can use any disk image writer (dd or rawrite for example). ADF is just 1:1 disk image, no conversion of any kind is needed.

[Piru]

if the disk writing works (Catweasel for example)

Of course it does not work with the standard pc controller!