I suggest you split you document using Insert-Break-Section Break - Next Page
Goto the part before the new break, select View - Header and Footer.
Swap to Footer
(use switch between header and footer on the Header and Footer toolbar)
Click the Insert Page number icon '#'
(You can adjust the position with Tabs (there are default tab positions in the centre and left side) or use text align buttons.
On the Header and Footer toolbar select Show next.
The dotted box around the footer will show 'Same as Previous'
Click the 'Link to Previous' icon on the Header and Footer toolbar.
The 'Same as Previous' text will disappear.
Select the page number, right click and select 'Toggle field codes'.
Place the cursor before the closing curly brace and insert page number from from the Header and Footer toolbar again.
Right click on this second page number and 'Toggle field codes'.
Edit the field text to the following, taking care not to erase any curly brackets as entering them again from the keyboard does not work.
Right click and 'Toggle field codes'.
You may have to Right click and 'Toggle field codes' a second time - depends on exactly what was selected the first time
Your new numbers will show.
In this example, pages after the break start 10 pages on from the last page before the break