Railworks America

I'v just discovered that all the manuals that you have accumulated can now only be opened using a document converter. An ad pops up offering to sell you The Doxillon Document Converter from NCH Software for $29.95.
Fortunately there is a work-around. In your search engine type in Doxillon Document Converter and you will find a free version for non-commercial home use. Its a bit clunky to use but it does work and its better than paying out $30 for something that was always free.
Brian Wilson.

Ooooooooh boy.
This smells so fishy that people in my office are complaining and opening windows.
Stop everything and start scanning your system with an up-to-date anti-malware program.

There MAY be legitimate reasons Windows now wants to open your PDF files with this program, e.g. you may have made a mistake and selected it as default program. This is easily fixed: right-click on a PDF manual, select "open with", select "Choose default program". In the new window, find and select your normal PDF viewer (usually Adobe reader), and make sure the "always use" box is checked.
You may (and should) now uninstall the other viewer.

There's something fishy alright.
I can still open mine with a PDF viewer.
I highly recommend running a scan with a free version of Malwarebytes.

I did a Google search and apparently it's supposed to be a legitimate program, but it gets very low review scores.

Sorry, this has everything to do with the program associations and software that is / isn't installed on your machine. No change in train simulator or the file formats.

Thanks everyone for your comments.
A few moments of thought on the matter should have clued me in to the realization that this was a simple matter of a corrupted/deleted file association; I don't know how this happened. I deleted the document converter ap and re-established the proper file association for .pdf. I also ran Malware and got no hits; something I should have been doing anyway.
Thanks again; problem solved.
Brian.