This complaint goes back to Windows 3.x or earlier. Not all apps remember old window sizes and each app may have a different fix so I can't be sure if the usual helps.
1. Resize the open app to the size you want (not full screen though for some odd reason) and then exit the app.
2. Try the ideas at https://www.google.com/search?client=opera&q=run+app+full+screen+windows+10
3. In the shortcut properties, look at RUN and change it to full screen or other.
4. In a pinch? AutoIt can do a lot here but you have to invest the time on AutoIT. AutoIT (found with google) can launch the app, then resize and move it to the screen spot you demand.
Pages only open to a 1 inch by 2 inch box.