Explain Everything uses a document viewer used in most of the apps. There are some cases when it does not interpret a document correctly and display some limitations. Mathematical equations, transition effects & animations, and some fonts will not be imported.
In some cases there may be some problems with a PPT/PPTX/Keynote files being incorrectly divided on slides or when various objects from other apps are embedded inside them. In general, if a PPT/PPTX/Keynote presentation does not import correctly, please convert it to a PDF file, and then import the PDF to Explain Everything. On a computer, you can print almost any file as a PDF by going to File -> Print. Almost all other operating systems have PDF creator tools which you can easily search for.