If you are having a presentation, save your PowerPoint file as
.pps file by going to:
File > Save as > PowerPoint Show (*.pps)
Now, your PowerPoint file will directly start the slideshow when you open it again for your presentation.
If you already have a saved PowerPoint file in
.pptx format, then just rename it to
Note: In case you are sharing the file with someone, its probably better to leave them in
.pptx format as it might annoy others when it opens directly as a slideshow.