I used to do this kind of stuff all the time. A search and replace like the one you're describing can be done easily using any version of Corel WordPerfect.

Find: .
Replace with: .[Hrt]

[Hrt] is the WordPerfect character code for carriage returns.

Posting a reply in case anyone else lands on this from a search engine the way I did.

Use EditPlus!

Copy the character you want to search, and then in the Replace box, click the little drop-down arrow on the right of it and select New Line.

It will insert the \n character, not the escaped "\n" as does with Notepad or WordPad.

Here is a screenshot of the EditPlus editor:

Notepad2 has a regular expression search/replace allowing a replace of (.*?\.)[ ]* with \1\n creating newlines with periods intact. It's exactly like Window's Notepad with all of the little utilities you wish notepad had 😁

Before hitting the Replace All button:

After hitting the Replace All button you can see it properly moves the sentence to the next line:

In XP's version of Wordpad, go to View, Options. You can set all the wrap settings there. I imagine it's similar in other versions.

If you don't already have it, download HTML-kit. It's free.

Open the file in HTML-kit, then run HTML Tidy (The F9 key).

HTML tidy cleans up the wrap thing and you may be able to copy and paste it into Wordpad or Word or whatever and get to where you want to be. When you open the file it should quickly do line breaks on the text, then just copy it back into Wordpad and save it. It's a shot in the dark but it may work.

By the way, when you try to open the file, you may have to change it to "all files", but if I remember correctly it will pull up text files.

You may want to do this in Microsoft Word. You can do a find and replace using . in the Find box and .^l (lowercase L) in the Replace box. This will insert a line break after each period.

If you want to simply put a new line in where each full stop occurs, you could do this programmatically with Java. Here is the script to use:

import java.io.*;

public class ReturnScript {

	private String filename = "test.txt";	// edit this
	private String outfile = "test2.txt"; // edit this
	private String find = ".";

	public ReturnScript() {
		try {
			BufferedReader br = new BufferedReader(new FileReader(filename));
			String data = "";
			String temp;
			while((temp = br.readLine()) != null) {
				data += temp;
			}
			br.close();
			BufferedWriter bw = new BufferedWriter(new FileWriter(outfile));
			java.util.StringTokenizer st = new java.util.StringTokenizer(data, find);
			while(st.hasMoreTokens()) {
				bw.write(st.nextToken()+System.getProperty("line.separator"));
			}
			bw.flush();
			bw.close(); 
		}
		catch(Exception e) { System.err.println(e.toString()); }
	}

	public static void main(String[] args) {
		ReturnScript rs = new ReturnScript();
	}
}

You will need the Java SDK installed. Compile the above code and run it, substituting in the appropriate filenames of your input file, and the file you wish to use as output.