Rigol unfortunately uses their own proprietary binary file-formats on the DP800-series. Couldn't find any converters, so far, but most file-formats seem to be quite straight-forward and some (including .rof-files) are documented in the attachment below.
In particular for .rof-files you can even get along without writing a converter: just strip off the 16-byte header at the beginning, dump everything else as 4-byte values to an ASCII-text-file using your favorite hex-dump tool and then import into Excel/LibreOffice/etc. . Please note that DP800-series at least up to FW 1.09 can't seem to write .rof-files longer than 131072 data samples, though.
BTW: The document below is in fact more or less directly from Rigol. They are really helpful when you ask them for further documentation, release notes for Firmware, etc.
Hopefully such useful information will be included in future revisions of the User Manuals or Programming Guides directly.