If I have a root CA certificate and an intermediate certificate, how do I merge them in to one file to use?
Firstly, export them in PEM format. PEM is a plain-text format, and all you need to do then is to copy the contents of the two files in to one text file, using your favourite text editor.
When you're done, the file contents will look like this:
[contents of intermediate certificate]
[contents of root certificate]
Retrieving data ...