Hi,
Add following code in [Alfresco_Home]\tomcat\shared\classes\alfresco\web-extension\share-config-custom.xml file
<blockcode>
<!– Document Library Actions config section –>
<config evaluator="string-compare" condition="DocLibActions">
<!–
Action definitions
–>
<actions>
<!– Download document –>
<action id="document-download" type="link" label="actions.document.download">
<param name="href">{downloadUrl}</param>
<!–
Evaluator to Disable Download action when document is locked by a user
–>
<evaluator negate="true">evaluator.doclib.action.isWorkingCopy</evaluator>
</action>
</actions>
</config>
</blockcode>