How to make text with 5000 people's names

If you need to go that character replacement route: do the replacement with InDesign's Find/Change function.

Then copy the text back. You only need to be careful to use only spaces that Illustrator can deal with.

My earlier demo used a clipping mask, but you might have noticed that when I created the clipping mask, a message appeared warning that the clipping mask might be complex enough to cause output problems. I realized that this might be avoided by using a different method. In the demo below, there are again two copies of the text frame set to different colors, but the upper layer (white text) is restricted by an opacity mask made from the large type.

So, using an opacity mask is an alternate and possibly simpler solution that might have a lower chance of causing a production problem. Another advantage of using an opacity mask is that the large character does not need to be converted to outlines, it can remain editable text.

Below is a demo of one way to do it completely in Illustrator, in only a minute or two, including Monika’s great ideas.

1. Paste your list into a text frame. 

2. Select a paragraph return. I enabled Show Hidden Characters to see it more easily. 

3. Copy the return character, choose Edit > Find and Replace, and paste it into the Find field. 

4. Click the Replace All button to instantly replace all return characters with em spaces (or another space character that you choose to distinguish names), and make sure paragraph alignment is justified. 

5. Copy the entire text frame, and paste it in front of the large character layer. (The large character was converted to a graphic object in advance using Type > Create Outlines.)

6. Select both the text frame copy and the large character layer, and choose Object > Clipping Mask > Make. 

7. Adjust the color of each copy of the text frame, as needed. 

For a more professional look, I should have also adjusted the letter and word spacing in the Justification dialog box, as Monika suggested.

I'm not sure where exactly your problem is? Writing 5000 names? Pulling that from a database?