I'm trying to reimport some updated word documents. Is it possible to reimport it without mentioning the Document IDs (I want each file to identify and update the correct document with the help of file name).
the gateway only support a re-import with a given ID.
As "file names" do not exist in the Document framework and even if they would they wouldn't be unique, the document's ID is the only way to specify the target of your reimport.
Depending on your Parser and gateway-configuration you can either enter the ID manually in the import wizard, or let the parser find the ID inside the Word Document.