This might sounds a bit unusual, but there might be a good reason why you would remove the first three characters of each line of an extensive Word document, such as numbering.
To achieve this, simply use the “search & replace” function :
Edit > Search > Search and replace
Then in the search field, add the following :
Leave the replace field empty and press the “replace all” button.
You can tweak the search string “^#” as you want to feet your needs, such as if you have lines like this :
10. Some text…
The search string would need to be “^#. “.