The most comprehensive is to import and export in SimaPro database format, especially if you want to exchange projects.
You can export files in SimaPro CSV, EcoSpold1 and ILCD format (not PEF compatible) as well as TXT and XLS(X) files. Note ! Only processes, not projects, can be exported in EcoSpold 1 and ILCD format.
You can import individual processes, product stages and methods in SimaPro CSV format. The EcoSpold1 format (XML) is supported but is rather complex and requires additional creation of mapping files.