<aura:component controller="openfile" implements="forceCommunity:availableForAllPageTypes">
    <aura:attribute name="currentContentDocumentId" type="String" default="06928000005l5I4AAI"/>
    <p>{!v.currentContentDocumentId}</p>
    <ui:outputURL aura:id="url" click="{!c.openSingleFile}" label="Click here"
                  value="{!v.currentContentDocumentId}"/>
</aura:component>

//JS controller
    ({
        openSingleFile : function (component,event){
            alert('hihih');
          var action = component.get("c.openfile1");
            var fireEvent = $A.get("e.lightning:openFiles");
          action.setCallback(this,function(actionResult) {
              //alert('inisde');
              //alert(actionResult.getReturnValue());
            var state = actionResult.getState();
              var id=actionResult.getReturnValue();
              alert(id);
              if (component.isValid() && state == "SUCCESS"){
                  alert(state);
                  component.set("v.currentContentDocumentId",actionResult.getReturnValue());
                  }

          });

     $A.enqueueAction(action);
       fireEvent.fire({
                    recordIds: [id]
                });

    },
    });

//Server side controller
public with sharing class openfile{
   @AuraEnabled
    Public static id openfile1(){
        system.debug('hihi');
        ContentVersion Cvid=[SELECT ContentDocumentId FROM ContentVersion where ContentDocumentId='06928000005l5I4AAI'];
        system.debug(Cvid.ContentDocumentId);
        return Cvid.ContentDocumentId;
    }

}

<aura:component implements="flexipage:availableForAllPageTypes">
    <aura:handler name="init" value="{!this}" action="{!c.openSingleFile}" />
</aura:component>

({
    openSingleFile : function (component,event){
        var fireEvent = $A.get("e.lightning:openFiles");
        fireEvent.fire({
            recordIds: ["069500000033oBoAAI"]
        });
    }
});