Force of habit more than anything. For a program to touch anything outside of the current user profile you normally need admin rights. I didnt test it under a restricted user.
But it is easy to change

Edit the file EnvelopePrinter.exe.manifest with notepad. This file is sued to tell windows what extra stuff the program needs, such as running under admin. I dont compile it with the exe like other programs do, this way a user can edit it if needed.
Once it is open in notepad just remove this
<security>
<requestedPrivileges>
<requestedExecutionLevel level="requireAdministrator" uiAccess="false" />
</requestedPrivileges>
</security>
Then save and you are done, you may need to reboot, maybe not. Sometimes windows keeps the manifest in cache and wont reread the file again till reboot.

After you remove that it will no longer ask to be run with admin rights.
Shane