knowing that I I can't use external libraries in Access
If you don't use the PowerPoint library then you are stuck.
Part of the difficulty is that you will have trouble doing this directly because of what you use as a file output format. Once a report is output as PDF then you need an Adobe external library to break it apart. The Excel output format is no better because I believe the pagination format is virtual, not physical. HOWEVER, if you output the report to either WORD .DOCX format or .RTF format, it would then be possible to open a Word application object and read the report.
Using VBA you could find the first character of the file, then find the next page-break. Declare a range between that first character and the last character before the page break. Output that range to a separate file. Now move to the first character after the page break, and find the NEXT page break. Output that page. Repeat the above process until you reach the end of the report file. Now you have however many pages were in the report as separate WORD files. Open the PowerPoint file as an app object, create a slide, and do a file insertion on that slide anchored to the top-left corner of the slide. Add another slide, insert the next file in sequence. Keep doing that until you run out of separate files.
I can't show you code for that because while I basically understand Office VBA, I've never played with that combination and it might take me a while to research it. But that is the general idea.