# EDI File Extensions

<table border="1" id="bkmrk-extension-type-.ddo-" style="border-collapse: collapse; width: 100%;"><colgroup><col style="width: 50%;"></col><col style="width: 50%;"></col></colgroup><tbody><tr><td class="align-center">Extension  
</td><td class="align-center">Type  
</td></tr><tr><td>.ddo</td><td>Invoice file ready for loading (single invoice only)</td></tr><tr><td>.dd2</td><td>Invoice file ready for loading (can support multiple invoices in one file)</td></tr><tr><td>.rtf</td><td>Return file ready for loading</td></tr><tr><td>.rtd</td><td>Return file that has been processed and will be transferred back to XChangeIT</td></tr><tr><td>.bak</td><td>A ddo,dd2 or rtf file that has been loaded into Computerlink</td></tr></tbody></table>

NOTE: Nothing is changed in a ddo, dd2 or rtf file in the process of loading into Computerlink. This enables these files to be easily reloaded by changing the .bak file extension to the original extension.