Please can you any one help me. I need to add new command to attach file with file or folder on alfresco some time I need to attach image or file with Document or folder same the command add Item in workflow.
Do you NEED it to be an action (same place as "start workflow" action)? That would be possible, of course, but more work than necessary.
As Mits stated, the best way to do that is with associations. If you create your own aspect declaring an association, then any node with that aspect will have an extra field in "edit metadata" where you can just select an other document you want to link.