ArchiCAD 14 (and 15) can read files from versions 8.1 onwards:
http://www.archicadwiki.com/ArchiCAD%20versions
Nobody should have files in 8 format since 8.1 was a free upgrade, basically fixing tons of bugs in 8.0 But, if you do actually have an AC 8 file, you'll have to download a copy of AC 10 or 11 to do an intermediate conversion.
All of the steps to migrate a project are in the beginning of the AC 14 Reference Guide PDF in the chapter "Migration Guide for ArchiCAD 14".
Cheers,
Karl
AC 28 USA and earlier • macOS Sequoia 15.3, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB
One of the forum moderators