Unfortunately, the '[' and ']' characters have a special function in wildcard usage, so trying to change them while using the wildcard feature is a problem.

Try the following:

With the wildcard feature unselected, use Replace to change all your '[' characters to something that is not generally found in your document. Perhaps XxX, or @-@. Then do the same for the ']' character.

This should turn [1] into XxX1XxX and [100] into XxX100XxX, etc.

Now turn on the wildcard option, and use Find/Replace for XxX*XxX. This will find any string enclosed within the XxX characters. If you leave the Replace box empty, you should delete all the old page numbers in your scanned document. (Assuming you have used OCR to convert it to text.)

I suggest that to begin with you use 'Find Next' and Replace individually, just to be sure your document does not have other strings of text enclosed in [] brackets or you might loose some important content by mistake. Only use Find All when you are confident...