How to disable Download Action in Document Library when a document is locked for offline editing?
Using Evaluator: evaluator.doclib.action.isWorkingCopy (An OOTB evaluator which checks whether a node is a working copy or not), we can configure Download Action to be visible or not in the UI.
Add the following entry in Alfresco_Home/tomcat/shared/classes/alfresco/web-extension/share-config-custom.xml file.
< !-- 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 >
     For more info, refer following link: 
     OOTB evaluators: http://wiki.alfresco.com/wiki/Document_Library_Predefined_Evaluators
 
