i have multiple pdf files with random number of pages like 1st file have 50 pages, 2nd have 73, 3rd have 14 etc.
i want to arrange 2 files on 1 page and paper is size a3 for example
1st page of 1st pdf file on right side of page and 1st page of 2nd pdf file on left side in a3
just like that
2nd page of 1st pdf file on right side of page and 2nd page of 2nd pdf file on left side in a3
and so on.
You're literally looking to build an imposition solution... you don't need to reinvent the wheel, there are plenty of software already available for that.
Corel also does have basic imposition features built in.