I know that the Pdf-viewer in Chrome and MS-Edge is basically an open source extension based on PDFium. I have read along the internet attempts of people trying to customize the built-in pdf-viewer e.g. changing the background color for a friendly night reading, trying to add new buttons to the UI, new context menu, etc. Most of them have a similar approach: Modify the existing plugin on the go and make the changes persistent. For instance, injecting javascript code to serve their purposes. The recurrent solution given was "Why bother? Go and use Pdf.js" but that implies to start a UI from scratch so for most people (me included) is not an option.
I don't know if it is possible to get the original source code of the extension used by Chrome or Edge (is it open source, right? so...), customize it, recompiled it and make it default in Chrome/MS-Edge. BTW, my target is MS-Edge because I have been programing other routines in C++ that I need to integrate to it.
Thank you in advance!