Enable debug logging with setDebugLog() to troubleshoot the cause. In general, our converter can't download external images, stylesheets, and JavaScript if:
Here are possible workarounds:
You can zip all external assets along with the HTML document and pass the zip file to one of the convertFile...() API functions.
If the assets are accessible on the public Internet, you can refer to them using absolute URLs:
<img src="https://example.com/images/image.png">