ViewerJS - Firefox not displaying text

[GreatNeighbours]

I mistakenly left put this issue on pdf.js forum and got abused.

Configuration:

Web browser and its version : Firefox
Operating system and its version: Win 10 upto date
ViewerJS version: 0.5.8  - This seems to be a very old viewer but is listed as the latest on the webpage viewerJS.org
Is a browser extension:

Steps to reproduce the problem:

1. We use a simple iframe to display a PDF document within ViewerJS, nothing fancy (src = "/ViewerJS/?zoom=page-width#../Uploads/EDocPro/EDT-21072022-163634.pdf"
2. PDF opens and displays what I guess is a template/image background used by the supplier without the Invoice particulars

If I open with Acrobat or Acrobat Reader or the https://mozilla.github.io/pdf.js/web/viewer.html it displays correctly with the full text

As the PDF is not ours but something supplied to us we have no control over the fonts etc (I presume its something like that), is there an update to the pdf.js code that we can add to the ViewerJS folder ?

What is the expected behavior? (add screenshot) - This is what the document actually should be
image

What went wrong? (add screenshot) - This is what is displayed in Firefox
image

PDF.js commentators suggested viewerJS was no longer actively supported but this forum suggest otherwise ?

[sylvestre]

For reference:
mozilla/pdf.js#15207