It can't. We considered adding this as a separate option when we implemented OA-PDF retrieval but decided against it, and I believe this is the first request for this we've gotten in the couple years since. We have a general goal of relying on data from more sources than just the site you're currently on — e.g., if Zotero detects a DOI on the page, some or all of the data might come from Crossref, not from the site you're on — and this fits in somewhat with that.

You can disable PDF download in the general tab of the preferences. The above question was about separately disabling PDF download of files from Unpaywall, i.e. typically not the "official" copy.

I found this old discussion while searching for a solution for the same problem. I would also very much like the option to turn off automatic downloading of PDFs from alternate sources.

The reason is that, at least for economics papers, the alternate version is often an earlier working paper version, and there's no way to tell how different it is from the published version. This means that every time this happens, I have to manually delete the automatically downloaded PDF, and then go back to the journal page to download the correct version. Additionally, I often don't notice this until I sit down to read the paper after I've transferred it to my e-reader. This has been breaking up my workflow quite a lot recently.

Yes, I know. But my problem is exactly the same as the original poster - sometimes I forget to "accept conditions" on JSTOR before saving, and sometimes it fails erratically for other reasons.

My point is, I would much prefer if I could disable the option to get the PDF from other sources, since most of the time I get the wrong PDF that way (i.e., an earlier version of the paper). I commented here simply to support the original poster's suggestion.

That said, I'd like to thank you for the tremendous work you've put into Zotero, which is a crucial part of my work flow!

@vmarinkov: There is a notification. It should say “Open-Access PDF” in the save popup.

Sometimes Zotero downloads the open-access version even when I am on the journal page and the actual PDF is available without having to log in.

Separate from any pref, you should obviously report any examples of this in new threads.

I've encountered the same problem: instead of an article, an ancient draft is downloaded.
This behavior makes the Zotero useless, because open-access articles are already available on the Internet.
Оnly copies of closed-access articles really need cataloging!

@dvoprm: This is all explained above. You can't currently disable downloading of open-access files specifically.

You can disable PDF downloading in general when saving from the web — that's "Automatically attach associated PDF and other files when saving items" — but that doesn't have anything to do with Find Available PDF.

I too would like to request a way to disable the silent download of an open source version of the paper. Often the open source Arxiv version lacks the revisions implemented in the peer-review process. It is most irritating when I have to manually replace the automatic download with the official pdf.

The root cause appears to be a failure of Zotero to detect that I do indeed have access to the official version. Perhaps this is due to a CAPTCHA test or an embedded pdf viewer, or maybe interference from an aggressive adblocker.

The simplest fix I can think of is a confirmation dialog box that would ask if you want to download the open source alternative with the possible answers of: yes/ yes (always) / no / no (do not ask me again)