The Knowledge Importer is a tool that allows you to import articles from CSV files into Lightning Knowledge. However, it does not support importing file attachments from external knowledge bases. To migrate the file attachments, you need to use the Files Related List on each article to add files to your articles manually. You can upload files from your computer or select files from Salesforce or an external source such as Google Drive or Box. Verified References: [Import Articles into Lightning Knowledge] and [Add Files to Articles]