I've downloaded and tested the Smart Label Creator and it supports loading SL files as the primary file format where the labels are stored as well as SLBK for the backup labels. The only Import function that I've found is related to the Database and it allows you to import CSV, TXT, MDB, and XLS files. I've downloaded the latest version and checked the Help section. You should do that too using Help > Help. Once the Help window is opened, switch to Search and type Import.