In earlier versions of ArchiCAD eg 7.0, it was possible to save an archive project in a lower version. This is now not possible in 8.1. I would like to save down to 8.0 to be able to share with my collegues who are still using 8.0.
The purpose of an archive is to guarantee permanence of library parts by encapsulating them with the project file.
In future, opening the archive also opens a special library with object elements contained in an independent library folder.
You will share your file by saving it as an 8.0 project and sending it to your stooges.
You will save your 8.1 file as an 8.1 archive and re-open it, sending the tidy library it makes to your colleagues separately. Instruct them to specify this library when opening the file.