BLOB fields

When you use the C/AL functions IMPORT Function (BLOB) and EXPORT Function (BLOB), a dialog box is provided from which the user can pick the BLOB to import or export.

Based on your selection, only the appropriate file types are shown. For example, if you select Bitmap, only files with the extension .bmp are shown. If you select Memo, only files with the extension .txt are shown. If you select User-Defined, all files are shown.

Reference