Revisting an old Adobe Acrobat Reader DC problem that clearly hasn't been solved yet, at least not in version 2021.007.20095.
We have a couple of servers producing PDF documents that are being emailed to customers. The PDFs are produced using Adobe Distiller 7.0, quite old but worked perfectly under Windows 7. After upgrading the servers to Windows 10, that is no longer the case. At times, PDF documents are produced with odd fonts names, e.g. ''CJIBJN-ArialMT", which Reader cannot find and cannot match so it produces a document with dots instead of text wherever that font is used.
Sadly (for Adobe) Chrome, Edge and FoxIt opens and displays these documents just fine. FoxIt replaces the strange "CJIBJN+ArialMT" font with FoxIt SansMM which works just fine. Acrobat Reader, instead, displays (in Document Properties) "Unknown font" and the dots mentioned above,
A last piece of information about this: if I open the file AppData\Local\Adobe\Acrobat\DC\AdobeSysFnt21.lst and change "FontName:ArialMT" to "FontName:CJIBJN+ArialMT" I will still get the same error message when opening the document in Reader but now the document will display correctly. It seems to me that the strange "CJIBJN+" prefix is added by Windows 10, maybe as a locale marker, whenever Win10 thinks that a document requires support of non-Western characters. But that's just a guess, I have no idea what CJIBJN really means.
But please fix this, we're getting lots of complaints from customers using Acrobat Reader to view the documents. Surely it can't be too hard, just do some kind (any kind) of font mapping and not just "Unknown font" and dots. Anything is better than dots really.
For now, we're advising our customers to use Chrome or FoxIt instead.
I am surprised that you have no answer yet for your issue but i want to confirm that i also have the same problem after some update that Adobe Acrobat Reader DC did.
Before some time ago i could read (with Adobe Acrobat Reader DC) my document with no issues and suddenly all the characters became...dots.
I read your post and tried Chrome and FoxIt, both are displaying the document with no issues at all so i am convinced that something is wrong in one of the last updates that Adobe Acrobat Reader DC did and not at the document.
I was able to resolve this when it happened to me while using SourceSansPro. I had to select all boxes of text within InDesign, where I had noticed the errors occurring in the PDF, and remove the CAPS, LIGATURES and select TABULAR LINING thats found in the Flyout menu of the Character Window. It's an OpenType issue, apparently.
The error MESSAGE still pops up when opening the PDF, but no errors are visible.