In the old days, things were different. How different depends on how old the days are. It's hard to anticipate every issue you might encounter in an old project. The first question is, what do you need from the project? Do you need drawings, a detail, or are we actually resuming work on the project?
If you just need to print a set, visit the plot or PDF archive of the project. Plot files can be placed as drawings in layouts in order to print them.
If you need a detail: Save the detail as a module before bringing it into a current project. If obsolete objects are used in the detail, I recommend replacing them with current versions. Keeping obsolete libraries loaded invites errors. And old objects are lame.
When you bring in geometry from old projects, it is very likely that you will get obsolete attributes (especially layers). These attributes should be deleted and replaced by their current versions. If you don't know how to do this, ask.
If you are resuming a project that has been on hold: Open the project in the current AC version. Generally, working in the current version is always better, even if you have to make some adjustments. The exception to this at the moment is that Archicad 16 projects should be finished in that version. Migration from 16 is burdensome because of building materials and wall inside/outsides.