How to display Doc or pdf file in datalist button

Do you mean you want to display the DOC or PDF file in a Datalist ASP.Net control? Or you just want to display the path of each document?
If you want to display the path of each document or file in the Datalist, I think the following two links might help:
https://msdn.microsoft.com/en-us/library/bb498210.aspx
http://www.w3schools.com/aspnet/aspnet_datalist.asp
But if you want to display the DOC and PDF files directly in the Datalist, you first need to find a way to load and display the document file on web. I think leadtools has an HTML5 document viewer control that you can use to support this feature. You can find an online demo here:
http://demo.leadtools.com/HTML5/DocumentViewerDemo/index.html

You can download the respective document and pdf file on click of a link. Refer any one of the links below:

http://www.aspsnippets.com/Articles/Upload-and-Download-files-from-SQL-Server-Database-in-ASPNet.aspx

http://www.webblogsforyou.com/how-to-upload-and-download-files-from-server-folder-in-asp-net/

http://www.aspdotnet-suresh.com/2012/02/saveupload-files-in-folder-and-download.html

Regards
Sneha