As to Allegro, once opened and saved in version 17, you can no longer open in previous versions - sort of like Solidworks. As to even older Windows for Orcad files (6.22 - 7) I had to go find an abandonware site that had the four installer floppys of Orcad 7.2 in order to open my files from the mid 1990's.

I have an old copy of Orcad 10 I use to bring stuff from Altium into Orcad. Orcad versions 16.6 and later will not open version 7 or older Orcad files (altium exports version 7). I have little issues in opening AD19 files with the older AD6.9. For hand builds I use an old addon called QualeCAD 9 no longer available) in AD6.9 that allows me to generate build sheets in PDF. Going from 99SE is a bit weird, but I've been able to backvert newer 19 designs to P99SE. I have an XP box that runs AD15 (last version for XP support) and I can open 19.1.7 files with little issues.

If you download the full installers for the various versions it will allow you to install on older OS's. I've tested installation on machines with dates well into the future and no internet connection. If you use the standalone license you get an ALF file.

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