Try running the DataExtractionUtility.exe that can be found in the openHistorian installation folder, typically C:\Program Files\openHistorian.
If you want to extract points for which you have no loner have metadata (e.g., all possible points) - this will require use of the openHistorian API to scan the target .D file and extract all possible data. At a low level, you can open the FileBlockHeader scanning each block, then find the associated file block and read the contents and then export to a file. The closest thing we have to this is the ArchiveIntegrityChecker which operates at this level.
Thanks,
Ritchie