How to add a second space

You might be working for the legal industry? Lawyers, oddly, have adopted an insistence on 2 spaces after a period (stop). I have never found out why they took this position, though.

I strongly recommend never to do it as it is a bad typographical error.  But to insert it, you can use find / replce, with GREP you can find exceptions. 

The easy answer is that you shouldn't do it. It's a habit from old typewriter days, and used in the US mainly. All typography books tell you not to do it.

But if you must, you'll have a hard time automating it. You'll have to work out whether a period is an end-of-sentence period or one after an initial, an abbreviation, or any other period that should not have two spaces after it.. Some algorithm may exist, you can try finding one on the web.

I forgot some important information. This is needed in many places in a large document. Most have two spaces already, but I don't want to have to go through 280 pages looking for the single space.