Not sure... but to me, this looks like your antivirus stripped off the ".exe" after the AC18-USA installation file... and so Windows is trying to figure out what program can open this incorrectly-named file.
Make sure that the downloaded installer is an .exe and sort that out. The normal installation will set AC 18 up as the default app for PLN files, etc.
If you've had this issue in the past... it is no doubt related to your antivirus, which should be temporarily disabled during installation.
One of the forum moderators • AC 26 USA and earlier • macOS Ventura 13.2.1, iMac Pro 10-Core, Radeon Pro Vega 64