.D00 File

The d00 file extension was in the past used for several audio formats based on Adlib and Edlib trackers.

Seems to be obsolete file format without support from the developer.

This d00 file type entry was marked as obsolete and no longer supported file format.

This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.

Files with d00 file extension might be old audio files in one of the Adlib or Edlib formats. 

How to open:

You should be able to playback these files using Winamp with AdPlug plugin installed.

How to convert:

Compatible tools may be able to export *.d00 files.