Version 10 can't open old LAY files - only up to version 9 can do this.
There is a big difference between the old multi-layout single page LAY files and the newer multi-page layout books.
This article might help you out.
http://www.archicadwiki.com/ArchiCAD10/ProjectMigration/Convert%20ArchiCAD%207.0%20and%20older%20pro...
But even if you do get these old files open saving is disabled in the demo version.
You might be able to print your PDFs though.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11