Very hard to say, depends on the articles and the field you're in. Rule of thumb I'd say around 250, but that can be several orders of magnitude off. (And just to be sure that's clear: that's for articles synced with Zotero file storage; there is no limit on the number of articles you can save locally with Zotero with a free account)
Thank you for the response, however I am not sure if I understood you well when you said 'that's for articles synced with Zotero file storage; there is no limit on the number of articles you can save locally with Zotero with a free account'
It would be really great if you could tell me the difference between the 2 and how it works.
I have a question regarding data protection when we upload pdfs from our local computer to Zotero's local storage. By doing so, does it gain access to all the local files at the moment of upload as well as later?
Firstly for clarity regarding terminology, "local storage" *only* means storage on your local computer, using its disk space. Uploading to Zotero servers - when syncing is ON - is not "Zotero's local storage".
Regarding your question, again firstly to to be clear, you don't choose to upload individual PDFs. Synced uploading is "all or none". So once *file* syncing is turned on, your PDFs (under Zotero\storage) will begin uploading to Zotero servers, in no particular order (up to your online file storage quota - at which point you will receive a message that you have reached your limit). So Zotero servers have access to your local PDFs from when file syncing is first turned on (of course you also need to be online). And the Zotero desktop program also has access to local PDFs even if file syncing is not on - it needs to be able to extract information from the PDFs. But that extracted information (metadata) is only uploaded to Zotero servers if you have *data* syncing turned on. https://www.zotero.org/support/sync
If you wanted to use Zotero server storage for some but not all of your PDFs, you could attach the other PDFs as "linked" files, remaining in a folder elsewhere on your computer (not the default "stored" PDFs under Zotero\storage; only those files are synced). Data syncing (if ON) to Zotero servers applies to *all* items (regardless of whether their attachment PDFs files are "stored" or "linked"). Note the limitations of linked attachment files discussed at this link: https://www.zotero.org/support/attaching_files#stored_files_and_linked_files
Upgrade Storage
(And just to be sure that's clear: that's for articles synced with Zotero file storage; there is no limit on the number of articles you can save locally with Zotero with a free account)
It would be really great if you could tell me the difference between the 2 and how it works.
2. Data syncing to Zotero servers is free and unlimited.
3. File syncing (eg PDFs) is subject to your online file storage quota (300 mb free; extra storage is paid).
4. You should also have good backups of your library.
See:
https://www.zotero.org/support/sync
https://www.zotero.org/support/zotero_data#backing_up_your_zotero_data
By doing so, does it gain access to all the local files at the moment of upload as well as later?
Regarding your question, again firstly to to be clear, you don't choose to upload individual PDFs. Synced uploading is "all or none". So once *file* syncing is turned on, your PDFs (under Zotero\storage) will begin uploading to Zotero servers, in no particular order (up to your online file storage quota - at which point you will receive a message that you have reached your limit). So Zotero servers have access to your local PDFs from when file syncing is first turned on (of course you also need to be online). And the Zotero desktop program also has access to local PDFs even if file syncing is not on - it needs to be able to extract information from the PDFs. But that extracted information (metadata) is only uploaded to Zotero servers if you have *data* syncing turned on.
https://www.zotero.org/support/sync
Zotero's privacy and security are outlined here:
https://www.zotero.org/support/privacy
If you wanted to use Zotero server storage for some but not all of your PDFs, you could attach the other PDFs as "linked" files, remaining in a folder elsewhere on your computer (not the default "stored" PDFs under Zotero\storage; only those files are synced). Data syncing (if ON) to Zotero servers applies to *all* items (regardless of whether their attachment PDFs files are "stored" or "linked"). Note the limitations of linked attachment files discussed at this link:
https://www.zotero.org/support/attaching_files#stored_files_and_linked_files