I believe this is a list of ActiveX controls that are installed on your system. To add one, install the corresponding application and it should pop up in the list.
Please note that ActiveX is outdated and not supported by modern browsers. What are you trying to add? There probably is a better way to achieve the same goal that is supported by browsers.
Thanks for pointing me in the right direction. The solution turned out to be a good deal more complicated on a Win 10 box. Services had to be started, IE security permissions reduced, Adobe Acrobat Reader DC installed and added-in to IE, and all that worked to allow the .htm help pages which referenced a PDF to work as expected when viewed directly within a .chm file.
However, in RoboHelp and IE 11 the display of the PDF hangs up with "Initializing". I am still tracking down how to deal with that. Any suggestions?
When embedding a PDF, avoid the ActiveX. Instead, try one of the following:
- Create a link in the TOC to the PDF baggage file. No need for a topic this way.
- Add an iFrame to the topic and point the source to the PDF baggage file. The browser will load the PDF using the built in controls.