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You should know this: https://community.ptc.com/t5/Mathcad-Tips/Official-PTC-Mathcad-15-and-Prime-1-6-End-of-Sale-Announcement/ta-p/818870
That tells you that you may be able install Mathcvad 15 on your windows 11 PC (although Mathcad 15 is not certified to work on that operating system), but to get its license activated, you need the PTC/Mathcad activation server which was put out of service a couple of years ago...
If you have (proof of) a perpetual license for your Mathcad 15, you might try contacting PTC support (that is NOT this forum) to find out if they can help you transfer the license.
Oh, and simply copying the files over is not the same as installing the program. You need some entries in the Windows Register as well, and must have the right prerequisites installed that Mathcad needs, but Windows 11 may not provide.
Be sure to keep the Win7 machine running, until you have a solution for running Mathcad 15 on Win11.
Success!
Luc
