Can I install an OLDER OS on my iMac?

I inherited my late father's iMac so now I have TWO of them. I need to run one on OS 10.6 and the other on the latest OS. Since my Finale music app and Adobe Acrobat 7.0 will not run on the new OS, I want to change the OS on the inherited iMac back from Yosemite to 10.6 so that when I need to use Adobe, I can just fire it up. I intend to upgrade my iMac, which is bigger, to the latest OS then and will just run Finale and Adobe on the older iMac. I realize that this is confusing and hope that someone can understand and advise me how to backward install an OS. Thank you.