Try Path>Union
If you lose the inside of the letters or squiggles, select just those areas first and merge, then select all and do Path>Union.
I just tried it because I had to remember how to do it!
I haven't done it in a while. If you select all and use merge, then you can't do union. So if you need to preserve the inside of anything (I hope this makes sense), select just those areas and do Object>Merge. Then select all of it and do Path>Union.
I just tried it several times and it worked beautifully. If there is an easier or more direct way I am sure someone will post it. Hope this helps - please let us know.