To add attachment(s) to a reference, go to Review > [Level] > [Form]. Scroll to the desired reference or use the various filters to narrow your selections. Click the desired reference to open it in the Review Screen.
Click the Actions button and click the "Upload Attachment" option. Selecting this option will open a "Click Here or Drag and Drop to Upload" window.
Using this method, you do not need to modify your document name to include the RefID. If there are multiple attachments, you will need to ensure the file name is unique to the selected reference.
If you wish to Bulk upload attachment(s) for multiple references, please refer to the User Guide for Uploading Multiple Attachments.