pdf file doesn't load: This XML file does not appear to have any style information associated with it. The document tree is shown below.

I had this same problem when I uploaded a .PDF to the resources section of my Storyline 360 project, created a button trigger to open it using story_content/external_files/(file name).pdf, but did not immediately save the entire project before publishing it. After publishing to Review 360, I got the XML file error message above. Upon reopening the Storyline project file, I found the document was no longer in the resources section. Uploading the .PDF to resources, saving and closing resources, and then immediately saving the entire Storyline project before publishing solved the problem.