There are in fact two different ways to do that.

Method 1:

- At the beginning of page 4, insert a section break (Insert > Break >
New Page). If there was a hard page break separating pages 3 and 4,
remove it to prevent getting an extra page.

- With the cursor on page 4, open the Header pane (View > Header and
Footer). On the Header/Footer toolbar, click the button to switch to
the Footer pane.

- On the Header/Footer toolbar, click the button to turn off "Same As
Previous".

- On the Header/Footer toolbar, click the Format Page Number button.
In the bottom part of the dialog that appears, type the number 1 in
the Start At box. Click OK.

- On the Header/Footer toolbar, click the Insert Page Number button.

Method 2:

Use this method if you don't need or want a section break...

- Open the footer pane on any page.

- Insert this field, using Ctrl+F9 to insert each pair of field
markers (shown here as braces { } although you can't type field
markers with those keys):

  { if {page} > 3  { = {page} - 3 }  "" }

This says that if the "real" page number as shown on the status bar is
greater than 3, the field result is the real page number minus 3 --
that is, page 4 will show the result "1", page 5 will show the result
"2", and so on. If the real page number is 3 or less, the field shows
nothing (the empty quotes).

After entering the field, press F9 to collapse and update it.

--
Regards,
Jay Freedman
Microsoft Word MVP        FAQ: http://word.mvps.org
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