Answer:
Yes, this is possible. When you select "All Files" for the file type in the "Open" section of RSTAB 7, the RSTAB 8 files will be visible as well. They can be opened.
A warning message appears because it is, of course, not possible to consider the features that were not contained in the older version.
Another possibility is to rename the file from *.rs8 to *.rs7 and open it directly. The warning message appears even then.
This procedure is the same for RFEM.
