Import of supplier attachments using Import Supplier Attachments FBDI template completes with error

Is there any restriction on the file type that can be imported for supplier attachments via FBDI e.g pdf , msg, doc, xlsx etc..

I have been trying to import file of the above types and the Load interface file for import completed with the following error :

There were no valid data files found in the zip file . Only .dat , .csv , .xml , .txt , .ack files are accepted for data files.

Please advise.

Version (include the version you are using, if applicable):

21D (11.13.21.10.0)