I have a file that is Adobe Illustrator 8 or older and I am getting error messages when I try to open it up.

Ubuntu 18.04
Inkscape 0.92

I receive the following error message when I attempt to open the file:

You need to install the UniConvertor software.
For GNU/Linux: install the package python-uniconvertor.
For Windows: download it from
https://sk1project.net/modules.php?name ... p=download
and install into your Inkscape's Python location

When I attempt to install python-uniconvertor from the command line, receive the following message:

Package python-uniconvertor is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'python-uniconvertor' has no installation candidate

That's correct. uniconvertor has been dropped from Ubuntu 18.04. You can get .deb packages for older Ubuntu versions here:

https://sk1project.net/modules.php?name ... p=download

and here:

https://launchpad.net/ubuntu/+source/py ... iconvertor

I think I took mine from here:
https://github.com/sk1project/uniconvertor/ (run python setup.py on the command line, in the directory where you unarchived the downloaded zip file)