If the 'space' between 'Page' and the number is not a standard space character, a Find expression relying on the standard space character won't work. Try with:
Page[!0-9]{1,5}[0-9]{1,3}
Basically, this says to find 'Page', followed by 1 to 5 non-numeric characters of any kind, then 1 to 3 digits.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]