Nexus 10 here running Kit Kat, and opening attachments are not an issue with a caveat.
Photos, and pdfs, are not a problem. Opening videos if flash based can be done with a workaround. Kit Kat does not support flash, but at least one browser using a modified apk for flash will run most flash content. There are instructions on the web as to how to go about getting flash content to run on Kit Kat. Do a search for 'Flash for Kit Kat' if that is your issue.