Powerpoint - applying the same formatting to text across all slides

Geuze

I wish to apply the same formatting to text across all slides in an existing presentation.

I know about View>Slide Master.

In that, I see the "default design slide master".

If I format that, e.g. line spacing, and then close Master View, the line spacing does not apply to all text in all slides.

Any advice?

smuggler.ie

Just to be sure your using Slide Master correctly i give you this
https://edu.gcfglobal.org/en/powerpoint2007/using-the-slide-master/1/
I found somewhat informative, despite irritating voice

Metric Tensor

I had to download a macro a few years ago to go through a PowerPoint document page by page and apply the formatting of the master slide to each individual page.

I'm afraid I can't remember the specifics of either the macro or what exactly it did for me. All I can remember is that I was handed a multi generational cluster f*ck of a PowerPoint file and I was trying to put some manners on it. I'm pretty sure I wasn't changing fonts or sizes, I was resetting page numbers and things like that - all the same maybe some similar macro might be available for your needs.