Zotero gives you two options for syncing PDFs across machines. One is to use Zotero's storage, which is limited to 300MB. The other is to use an external service using a protocol called WebDAV, which works with services like Box. You can use your DartBox account to sync your Zotero PDFs using these instructions. Dartmouth's Box service uses your Dartmouth credentials, so there are a couple of extra steps involved than there would be for a personal Box account.