While migrating to a document library you may receive the warning "No items were written to SharePoint when processing this document."
You can check the mapping rules on the Map Data tab.
If you are mapping to a word document or PDF, ensure that your mapping is correct and that the mapping is creating the file. If you are migrating attachments, make sure there is a mapping to a file attribute on the SharePoint side.
The File field mapping is required for a document library. If this does not exist there is nothing to actually write to the library which is why we get the "No items were written to SharePoint" warning.