AI, which is not guaranteed 100% accurate, offers this...
"In NCH Photostage, you cannot directly add text inside a speech bubble clip art as an integrated feature. Instead, the typical workflow is to first add the speech bubble as a clip art or shape, and then separately add a text overlay on top of or within the speech bubble by using the text tool.
To add text into a speech bubble in Photostage:
Insert the speech bubble graphic onto your slide.
Go to the "Text" tab or text tool.
Add a text box on top of or inside the speech bubble.
Type your desired text and adjust its position, font, and size to fit within the speech bubble shape.
This method overlays the text onto the speech bubble rather than embedding the text within the clip art itself, which is how Photostage handles text and graphic elements.
If more refinement is needed to integrate text and speech bubble as a single object, graphic design or comic-specific software might be more suitable, but for Photostage, the overlay approach is standard."
Or use Videopad... 