Powerpoint File Size Does Not Reduce Even After Deleting Slides

Updated 10 Jul 2018 - After some testing, I find that those "extra" template slides appear when you try to copy some slides and paste them to another deck with "Keep Source Formatting". So if you frequently encounter this problem, you could be like me, often having to take content from different decks and piece together a customized deck for the work on hand. If so, then the solution below should help with your Powerpoint file size.

If you work with Powerpoint slides a lot, you may have seen some pretty big and bloated slide decks, especially if it contains lots of photos or video content. This presents an issue when sending over email with attachment size limits. Most of the time, deleting slides or compressing content should help to reduce the size. 

If you had come upon this article after googling, you probably had just encountered a similar frustrating experience as me. Even after removing most of the content, the Powerpoint file size remains mostly the same. Most online posts revolve around talking about how to compress the ppt files or simply just deleting unnecessary content. Not many discuss why certain ppt decks remain stubbornly big even after deleting content. The only closest I could find was this Microsoft Community post which did not help much.

A simple workaround I found to reduce Powerpoint file size was to copy the slides into a new ppt and save the new file. Beware that even though I had Copy and Paste with "Keep Source Formatting", sometimes I would still encounter funny results, for example, shape sizes becoming distorted. So do check through your final slides before sending them out or using them for presentation.

Back to the topic on hand, it did not make sense that the Powerpoint deck would not become smaller after deleting stuff. So I did a little further test by deleting all the slides from the original slide deck and saving the file with another name. The file size of this "empty" ppt deck was roughly the size that was reduced, had I copied the slides to a new file.

So it became apparent that this "empty" file was not the problem. It was then that I realized where the issue was. As this was a corporate presentation slide deck, it came with a corporate theme. It was not immediately apparent but all the years of copy-and-paste by various authors had injected junk templates from other sources into the theme over the years of use. You would see these templates if you right-click on a slide to see the layout types available.

To rectify, go to View > Slide Master. This will show all the slide templates stored in this theme. For my case, I saw a lot of junk templates unrelated to the theme. Once I removed those that I did not want and save, the file immediately became a manageable size.

I guess that for convenience, people just kept reusing the base file by deleting all previous slides and start adding their slides. I still cannot fathom why those content would go into the base theme template, but next time you encounter big Powerpoint files that just would not become smaller, try looking at the theme first.


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