I have a 198 pages word file. I have to make page numbering in 20 first pages in I,ii,iii and the rest in 1,2,3, But the problem is that when I try to do so, it changes from page 21! Surprisingly. I don`t know what`s the reason.

To get different numbering schemes, you have to insert SECTION BREAKS.

1) Go to the bottom of page 20 and click on Insert > Break > Section Break Types > Continuous

2) Go to page 21 and open the footer for that page

3) Disconnect the "Link to Previous"

4) Click on Format Page Number and adjust your numbering for the new section... sometimes you have to start at "0" to get the "1" to appear in the right place