Hi,

Using document library when we upload a document suppose if we upload a pdf document . You can see a small pdf icon.

Based on the document type the icons will map in Default Document Library in SharePoint 2013.

Similarly we need to get that while doing programmatically for that we can make use of  SPUtility.MapToIcon

The original location of icons in the server will be at: C:\Program Files\Common Files\microsoft shared\Web Server Extensions\15\TEMPLATE\IMAGES

while in program the path will be like:http://doaminname:portnumber/_layouts/images/icdoc.png

string icon = SPUtility.ConcatUrls(“/_layouts/images”,SPUtility.MapToIcon(item.Web, SPUtility.ConcatUrls(objSPListItem.Web.Url, objSPListItem.Url), “”, IconSize.Size16));

Use Image Control in ASP.net

then

assign the

Image.Url=objSPListItem.Web.Url + icon;

Then you will get the icon related to the document type.

Note: SPUtility in sharepoint 2013 is a wonderful class which includes many useful methods.