No need to panic or uninstall
😉 (it won't do much unless you also run System Restore to restore your registry to where it was before the installation).
The problem sounds like InDesign has taken over the PLN extension.
You can still open these files in AC by starting AC first, and then using File Open to open the files.
But, here are a couple of methods to get the file association back to AC:
1. Easiest: Browse in Explorer to a folder containing AC PLN files. Right-mouse one, click Open With... and then - even if you see AC (!) - select "Choose Program...". NOW, select ArchiCAD (or browse if necessary), and be sure to put a check mark in the box "Always use the selected program to open this kind of file". Then click OK. Exit AC after it opens. You've reset the 'open' behavior for PLN files in the registry.
2. Tricker/easier to screw up: In Explorer, Click Tools | Folder Options, then the File Types tab. Set the appropriate info for PLN (perhaps by copying it from BPN).
Karl
AC 28 USA and earlier • macOS Sequoia 15.3, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB
One of the forum moderators