The files won't disappear from the cloud once they're there, so if you're sure they've been uploaded you can safely delete the local files by right-clicking on the file, choosing "Show File", and deleting the file that shows up. (Make sure you delete only stored files within your Zotero data directory, not linked files, which don't sync.)

One thing to be aware of: there are currently a few situations in which files might not be uploaded properly. Generally speaking, if you do a Reset File Sync History from the Sync->Reset pane of the preferences (but no other reset options!) and the next sync completes without errors, you can be reasonably sure that all your local files have been uploaded, but having a local backup of all your data and files is always recommended, even if you then delete the files from your main hard drive.

Future versions of Zotero should provide better ways of making sure files are online and offer automatic local file management (e.g., using only a fixed amount of space or keeping files for a fixed number of days since last open).

I am just now coming back to this discussion I started in August, because I finally have time to address this issue and I realize I have another question.

Dan wrote that I can delete the pdfs from my computer's hard drive as long as I'm sure they uploaded properly to zotero.org. So I am sure of that, but:

1. I've got a couple thousand pdfs. Do I need to right click on each of them and delete them individually? I'm hoping there's a quicker way to do this.

2. One a pdf is deleted, what happens when I click on it in the Zotero pane? Will it take me to the zotero.org site?

3. Assume this is all working and now I have a new pdf to add to my library. Should I do that as usually, allow it to sync, and then delete the local copy? Or is there a better/quicker way to do it?

I haven't found any documentation on these questions, but please do point me in that direction if I've just overlooked sources.

Many thanks.

Thank you for the quick and helpful response.