Combining multiple MPDs into a single file

[Forge]

I have created a number of what I would consider sub-models that I wish to combine into one larger model. The problem is that some of these sub-models are MPD files with their own sub-models, while others are the LDR files I would want. Is there a way to combine multiple MPDs together (since it would be simple to create MPD files out of the LDR files)?

I've spent a large amount of time creating these files (and perfecting the instructions for each of these sub-models), and now when I am finally ready to put these together to create instructions for the final assembly, I have run into the issue that I cannot figure out how combining the parts can even work.

As I'm newish to Ldraw, I only figured out that these sub-models I had created were of different file-types when I attempted to import all of them into one master file, but was unable to find several of the files needed, and realized this is because some are .mpd and others are .ldr

Is there a good method for solving this issue and combining the files into one MPD as I'd like?

Thanks!