Leylak de Caupenne

I've never done this myself, but I believe CHM files are compiled html files. So you probably need to either get the original source files, or decompile the CHM to get them.  Then translate the html and recompile the CHM.

HND are a similar sort of thing but I think support more formats, so it's possible to work from Markdown or DOCX for example.

Either way, I think you have some preparation work to handle first in converting to an appropriate format for a CAT tool.

Open such file in any text editor. In the header you should find the application which created such files. If this is Help & Manual (which I suppose), go to their webpage and download the test version. It will deliver you a file type, which works with Studio.