Hi Pravin,
We can have DMS connector installed and configured in SAP Portal using which we can view DMS documents in SAP Portal.
Please check whether you have such configuration in Portal.
Useful reference
http://help.sap.com/saphelp_erp2004/helpdata/en/32/2a840d132af04fa2f0b31ebf3e8a78/content.htm
Documents will be uploaded only from backend system which will be ECC . These uploaded documents can be viewed from SAP Portal as well.
Also check whether you have any iviews created in Portal which is used for SAP DMS.
Hope this helps.
Regards,
Deepak Kori