If you import citations from a text file you must select the appropriate Import Filter. Filters are files that allow you to import references saved from databases that do not have an automatic export feature. By selecting the correct filter, EndNote will transfer the information into the appropriate field in the EndNote record.
Import is the function, filters allow you to do it.
EndNote provides hundreds of Import Filters for a variety of databases and automatically stores the 100 most popular filters as individual files in the Filters folder in your EndNote program folder.