If you are trying to the download again, checking your browser's "Downloads" folder (Ctrl+J or Cmd+J) or your email "Sent/Received" history for the date you merged it is usually the best bet.
(e.g., in an email, a student portal, or a work dashboard) Download 57861576271167merged pdf
If you can describe the contents of the files that were being merged, I can help you summarize or write about that specific subject. If you are trying to the download again,