Did you know that there are great options to convert pdf files to Powerpoint?
And, they don't just convert each page as an image but actually recreate file w/text boxes, etc. Not perfect, but very good. Click this Google Search link to locate options: (I've used both "Smallpdf" and "Ilovepdf" and had great results.)
Once you have the Powerpoint, you can, then, easily, convert to Slides while uploading. (Just click the "cog" in the upper right corner of Drive, then "Settings" and make sure you have "Convert uploaded files to Google Docs editor format" checked as shown below.)
If you're trying to create a presentation from a pdf, these tools are lifesavers!!