I probably need to make a blog post for this, but for folks using the new external file support (docs here, https://developer.adobe.com/document-services/docs/overview/pdf-services-api/howtos/pdf-external-sto...), keep in mind that you have two ways of using this:
1) Supply an external URL for input and output (this is probably what you expect)
2) Only supply an external URL for input (you probably didn't expect this to work, I didn't)
In the second case, we will store the output as an asset (ie, our temporary system) where you can then download it using a GET request.
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