There are a few different places to get a Pro-Stitcher Premium (PSP) user manual. While in Pro-Stitcher, select the Information tab, then Help on the ribbon. This opens an interactive manual on your Pro-Stitcher screen that you can easily search. You can also tap the Help button (white question mark in the blue text bubble on the right of the ribbon) for on-screen interactive help.
The user manual is also available to download here: https://prostitcher.com/prostitcher/
Scroll down until you see the picture of the PSP screen on the right; underneath the picture you will links to download the PSP User Manual.