DRM & Open Source

Is the implementation of DRM in open source applications detrimental to the spirit of free software? Or do developers not even have a choice in this matter? Here's a reference to a discussion between KDE developers, building an open source PDF reader (KPDF), who are confronted with the copyright claim over the PDF specs by Adobe, which only gives permission for implementation if "reasonable efforts" have been taken to also implement (DRM) restrictions.