Open the first PowerPoint presentation
Go to the slide where you want to insert content
Click the Home tab
Select New Slide or reuse an existing slide
Click the arrow under New Slide
Choose Reuse Slides
Browse to the second PowerPoint file
Select the slides you want to add
Click Insert Slide
Repeat for any additional presentations
Save the combined file under a new name
Alternatively, open one presentation
Copy slides from the other presentation
Paste them into the first presentation
Choose Keep Source Formatting if needed
Save the merged presentation