My first thought was some kind of cross-platform PDF code that wasn't doing file coordination properly. But what you're showing is basic NSDocument file reading. However, NSDocument can get very complicated when writing. You said you're writing a viewer app. Are you sure you've specified the role for PDF as Viewer? There would have to be some other kind of change, possibly to attributes or permissions, in order for Time Machine to balk. Reading a file should be a no-op in that respect.
Topic:
App & System Services
SubTopic:
Core OS
Tags: