Reply To: Add (the same) 2 letters to every instance of 4 digits in a 45 page document

\d is a so called wildcard-metacharacter and will find all digits [0-9]. To find one or 50 you could use \d+. The plus-symbol is the metacharacter for one or more times. But you ordered a specific amount of digits: 4 > Therefore I use \d{4}. Because this will find also 4 digits in a 6 digits number, I use a so called anchor: (for word boundary).

\d{4}

Find the start of a number, 4 digits, end of a number. You can then insert everything with $0 in the change to field.

Kai