I have a multiple page file in which each two pages related to each other(they going to print back to back ie. 1-2. 3-4,...) & i want that each sets of pages get same page no. (ie. 1st page will have fontpage1& 2nd will backpage1 & continue for rest of...). I tried using two different master pages but it didn't work.
I'm not exactly clear about what you want. Are you saying that in a hypothetical 8-page document that your numbering will be:
2: backpage 1
4: backpage 2
6: backpage 3
8: backpage 4
If that's the case, it probably wouldn't be worth it to use the page number placeholder and mess with the Numbering and Sections options on every page. I'd probably just use manual numbering.