On the one hand, KDE developers may not have a choice -- Adobe claims copyright over the PDF spec, and grants permission to implement it only if there are "reasonable efforts" to implement restrictions in PDF. (See the spec here.) Since Adobe is the company that went after Dmitri Sklyarov for cracking the DRM in their eBook Reader, it's not unreasonable to believe Adobe would go after developers who implement a DRM-free PDF reader.
On the other hand, there are those who feel that there's a moral obligation not to implement DRM in free software.
As digital restriction management continues to proliferate, this is a question free and open source software developers will have to answer. What do you think? Should open source software implement DRM?