I've just found out (via a support ticket and simple repro) that in fact that support is still missing. Can that please be fixed ASAP?
The symptoms are: you build a Power BI Desktop solution including PDF files from a cloud source (e.g. SharePoint or a web site) and it refreshes fine. But after publishing to the web service, your web service refreshes will crash with a really awful message. It seems to indicate the developers messed up their build, e.g.
Could not load file or assembly 'Microsoft.ProgramSynthesis.Extraction.Pdf, Version=18.104.22.168, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference.