One may find that "Document Icons" are no longer displayed in search results after modifying the DOCICON.xml file. In this scenario an empty box will appear where the document icon should be displayed. The same document icons are displayed correctly while viewing the document libraries.
This issue can be caused by multiple file extension mappings in the DOCICON.xml file. To confirm this problem one can view the HTML source of the search results page and find the documents with the missing icons containing an empty source path for the “srch-Icon” class.
In this case although the values are different, all document icons will not be displayed in search results because there are two file extension mappings for “PDF” in DOCICON.xml.
To resolve this issue simply remove the duplicate entry for the file extension mapping in DOCICON.xml.
A modified DOCICON.XML file applies only to a single server, and must be copied to every server in a server farm for the icon to be displayed consistently. An IISReset command is required for the changes to the DOCICON.XML file to be reflected in a rendered page.
Service packs or hotfix patches can overwrite changes to the DOCICON.XML file. Therefore you should package the changes in a format that can be easily reapplied. This makes it less likely that your changes will be overlooked or applied incorrectly if they are manually updated later.