COMBINE Archives, is a standardized archive format, that can contain a multitude of files. A Manifest in the root directory describes the contents and their file format.
COPASI supports the import and export of COMBINE Archives.
If you want to try and run the files exported by COPASI with another tools, you might want to try the BioSimulations website, this will directly allow you to import the COMBINE archives exported by COPASI.
Simply run File\Export Combine Archive, and select a filename to save the current model under. By default COPASI will export:
Either drag and drop a COMBINE archive onto COPASI to open it, or select File\Import Combine Archive.
When COPASI imports a COMBINE archive it will look for files to open in the following order:
In case there are multiple SED-ML files in the archive, COPASI will ask which one to open.
For more information see the pages on importing SBML and SED-ML.