Sync eBooks across Macs (NOT iOS devices), purchased from third party sites

Is it possible to sync eBooks and PDF purchased outside the iBooks Store across your Mac computers? I have 2 Mac Books Pros I'd like to sync eBooks that I've purchased from third party book stores. I the same Apple ID setup on both Macs but it seems that ONLY eBooks purchased from the iBook Store are sync'd. Most of the articles I've read talk about syncing between Macs and iOS devices none seem to cover syncing between Mac computers.