As we all knows that rendering engine doesn’t support javascript generated elements. The following logic also will fail to redirect the user.
<apex:image url="{!$Resource.PDFImage}" onclick="window.open('www.google.com');" width="550" height="50"/>
The better approach here is the following line of code which works perfectly in this scenario.
<apex:page renderAs="pdf" >
<apex:form >
</apex:form>
</apex:page>
**Caution: Use https instead of http while referencing the link
Also as a best practice use images from static resources while rendering pdf