Earlier we were using pdfjs express version 7 for gettting stamp coordinates.
coord.VB, coord.rw, coord.sw, coord.Ur, coord.Vr
But in new version of pdfjs express version 8, it does have document to get these coordinates.
Those properties look like minified values, which change between builds. We recommend not accessing the minified values because of this reason. Here is a guide on our coordinate system: PDF.js Express Viewer Coordinates | Documentation
Web Development Support Engineer