Client sent me an xliff. A project was created when I clicked on (and opened) the xliff. 

I now need to add a new xliff file to the project. 

I've done this before, and as I recall it was fairly simple, so I don't know what the problem might be. Since I was unable to add the file, I duly looked for instructions.  

Here: 

https://gateway.rws.com/csm?id=kb_article_view&sysparm_article=KB0025756

I find: 

1. Double click on your existing Project, this takes you to the Files view.
2. Now from the left choose the source language.
3. Right click anywhere on the white space on the right side where the existing files are.
4. In the right-click menu you have Add Files.

I see "Add Files," but it is grayed out. 

What am I missing?

Thanks,