When you import a flat file in the Designer, the Flat File Wizard uses the file name as the name of the flat file definition by default. You can import a flat file with any valid file name through the Flat File Wizard. However, the Designer does not recognize some special characters in flat file source and target names.
When you import a flat file, the Flat File Wizard changes invalid characters and spaces into underscores ( _ ). For example, you have the source file “sample prices+items.dat”. When you import this flat file in the Designer, the Flat File Wizard names the file definition sample_prices_items by default.