Unless you are using a fixed width font that process is unlikely to work.

Replacing wide letters, such as w or m, or narrow letters, such as i, with x will alter the overall length of the text, resulting in the document being repaginated with the possible result that it will have fewer pages.

For detailed help on using wildcards in Word find see https://wordmvp.com/FAQs/General/UsingWildcards.htm