Select a pdf file in Finder and click the Command-I keys to display the Get Info panel. Click on the lock icon at bottom of the panel and enter your password. Then click on the "Open With" pull down and select Adobe DC and click the "change all" button. This sets Adobe as the default for pdf files.
You could use web services such as Zamzar to convert your PDF to PPT directly, but the downside is lack of privacy and watermark on your PPT.
It is better to split the process into two steps:
Export PDF into images
Import images into PPT
Export PDF into JPG using Preview
macOS' Preview has built in functionality to export your PDF into PNGs. Once you ...
If you only have one page you can open the PDF in Preview and then export the file as a jpeg. See image below.
Then you can paste the image into Powerpoint.
If the PDF is more than one page open it in Preview and select Thumbnails. Select each thumbnail and export it as a jpeg. Continue as I explained above.