Please help me on whether I can set different scale for each different page on the same file.
Example having 1:100 scale on Page 1 and 1:50 on Page 2 then 1:30 on Page 3.
I don't think that there is a built-in way to do that in CorelDRAW. Drawing scale is a document property, not a page property.
I think it might be possible to create a macro-based way of changing the drawing scale when a page is activated, but I don't know if anyone has already done that.
There are some forum discussions that include ways to more quickly and easily change the drawing scale manually.