In The Raiser's Edge, exports create MDB files and they can be used with Custom Reports (Crystal).  MDB is the file extension of a Microsoft Office Access database. Access is a relational database management system that’s included in the Microsoft Office suite.  

MDB files are also used for the source document  when Word merges fields from The Raiser's Edge. 

You can export using HTML as the file format in case you wish to add the data to your website.

You can delete these files if you wish.