Maybe. Is it easy? Depends on what parts of the PDF viewer from Chromium Electron contains and/or how easy it is to access native libraries from and app.
From briefly looking at the documentation, it sounds like they have a method for accessing the Flash plugin, so there might be access to the PDF viewer somewhere or at least an example to follow for implementing it.
PDFium is native C/C++ library, so it isn't going to be trivial to access, at the minimum you with need some sort of FFI in JS to bridge into it. This likely a question better suited for an Electron dev forum.
-Ryan Harrison