I am wondering if 2 applications can appear on the screen at the same time either side by side or whatever?
The reason for me to ask such question is that, let's say, when i scroll down the screen of my ADOBE READER application, 
the COREL PAINTER X application will disappear even though these 2 applications are being open concurrently (Picture 1 to Picture 2). 

That's indeed a very inconvenient and annoying experience when i am making some reference from both applications back and forth.   

 

when you scroll, you don't need to "active" that app

just move your mouse over the app you want to scroll, and scroll....

don't use scroll bar

track pad then use the two finger scroll
mouse then use mouse wheel/ball

so I never recommend ppl use apple's mouse....

which tablet you use? if it's wacom then you just need to assign buttons to scroll up and scroll down....

It makes me also wonder if i can scale down COREL PAINTER X (or other app. like PHOTOSHOP, ILLUSTRATOR) screen so that they can appear on the screen side by side  so that even though i am working on one app. , the other one is still shown on the screen and just left inactivated ?