Okay, but to go further with troubleshooting would require some information from your end as to what you have tried thus far?
I suppose I really should have started at my end with a question before I offered what I did, and that is whether any sort of Windows Update was done just before you noticed notepad was gone? Whether any security update or scan was done using a third party tool? Any sort of system change?
Actually, the Windows Update would likely only be of the security sort. I don't know if that other update program I paid for on one of my units is still running as I haven't been to that house for a number of months. This Win7 unit here at this work station only gets the security stuff updates.
One more thing, but pulling on old memory here, and my memory is slipping with age and the chemo, so might be unreliable. But I seem to remember that notepad was a favorite target of security related attacks, so that may be worthy of a thought --- maybe a BIG "may be".
But, even so, I wouldn't be too happy if a tool such as that just up and left the system. Of course, your unit may be the first case of true AI changing to be creative on its own and didn't like that software. If that proves to be the case you now have a one million dollar computer. Maybe worth more.