We have recently upgraded from LCA 2014 to TDX 2014. Previously, we could add a PDF file as a resource in a publication, create a cross-reference to this resource, and have an active link to the PDF in an XHTML help output.
In TDX 2014, the PDF does not get included in the XHTML help output folder when built, so the link does not work.
In LCA 2014 we could categorize the repository file as "Other (Word, PDF, ...)" while in TDX it's just categorized as "Other."