How do I substitute all text areas and prevent font change?

as Melissa said,  that looks like Illustrator you're working in.  If so, like she said, create outlines for the text.  Its an easy fix.  I would say that after that,  to save as a copy,  so you still have the original copy in case you need to edit the text.  But if it is Photoshop,  just flatten the image as JJMack said.

Do not send them a layered file.    Sent them a none layers tiff files if they want 16bit color or send them 8bit jpeg files.  Save your work in layered file so can make additional changes in the future without needing to redo all processing.  Your Printer will never get a text layer. They will just get a raster pixel layer.

You posted in the Photoshop forum, but from your screenshot you are actually working in Illustrator. You can outline your text. Duplicate you text layer and hide a copy in the layers panel - just turn the eyeball off. Select the visible text, Then go to the type menu and choose create outlines.

You could rasterize it, but he would lose the ability to edit the words.