In this web page you can find the extensions com.KIO4_PdfS10.aix and com.KIO4_Pdf10.aix.
Files are saved in ...
/storage/emulated/0/Android/data/edu.mit.appinventor.aicompanion3/files/ ... in emulation with Companion.
And...
/storage/emulated/0/Android/data/'namepackage'/files/. .. when Built.
Can you test if they work for you?
http://kio4.com/appinventor/284C_extension_crear_pdf.htm