I get the "forbidden" icon (and it does not get deleted)

- I was trying to drag pdfs (or whole refs) onto the trash (visible in the left menu under Zotero tool), and also tried to select pdf and press the delete key (this did not work either). But I think i understand things a bit better now: under Zotero, I found the right click and 'put to the trash' option; and under the web library I did what you recommended.
- That said, you are right, i was not admin (my status has now been changed by the owner of the list, which should help me managing the shared library). However, I want to mention that contrary to what you say, I managed to edit the refs and the files of the shared library even if I was not admin... I can see this because I have unfortunately put some mess in the shared library through my tries at removing some duplicate pdfs (I did these tries under Zotero and then under the web library, when I was not admin of the list).
This notwithstanding, it should be OK now thanks to your recommendation about the admin status. Thank you very much for your very clear explanations on all this.

- I have a further question if I may, because here is what I would like to be able to do ultimately: Is there a way to remove all the data related to shared library locally (on my disk), or all the pdfs/attachments, in order then to re-create this cleanly on my computer?
The reason why I am asking this is the following: We have a shared library that needs being tydied up (we have some duplicate ref and a lot of duplicate/triplicate pdfs within most ref items); the owner of the list is doing this from her Zotero tool; I want to participate in this cleaning through the web library interface. Then, I want to restart from clean my zotero on my computer, to ensure i don't eat up disk space unnecessarly. However, it seems that it is impossible to uninstall or clean the Zotero database cleanly on my computer so as to reupload it from the web library... Can you tell me if this is possible and how?

I thank you very much for your help,
best,
nathalie

Dragging items to the trash has never been implemented, so that won't work.

While you can use the context menu if you want to, the Delete key definitely works. To be clear, on a PC keyboard Backspace and Delete are not the same, and you need the latter. On some laptop keyboards, an actual Delete might require a modifier key.

However, I want to mention that contrary to what you say, I managed to edit the refs and the files of the shared library even if I was not admin...

That's not what I said. I said one of your groups is set not to allow that. The others are. But if you were trying to drag to the trash, this has nothing to do with permissions.

Is there a way to remove all the data related to shared library locally (on my disk), or all the pdfs/attachments, in order then to re-create this cleanly on my computer?

I'm not really clear your question. If you want to wipe out all your local data — from all your libraries — you can always just unlink your account from the Sync pane of the preferences, tell it to delete your local data, and then set up syncing again, and then resync all your data. But there's no need to do that unless there are local changes that you're trying to avoid syncing. Otherwise, if you're already fully in sync, any changes made remotely will just be applied to your local Zotero.

I want to participate in this cleaning through the web library interface

Why? If you're doing any sort of significant work, you want to be using Zotero, not the web library.

Then, I want to restart from clean my zotero on my computer, to ensure i don't eat up disk space unnecessarly.

I'm not clear on what this has to do with disk space.

I unconnected my account from the Sync pane of the preferences, but I did not find how to tell Zotero to delete my local data at this occasion

There's a checkbox when you log out that you can check to remove local data. But there's no need to do that — see below.

What I tried was to locate my local data on my computer disk and delete it myself but then got error messages when I set up syncing again, warning that my local database must have been moved and I should locate it again

That works too, and it's not an error — it's just warning you that you're syncing to an empty database, in case that's not what you intended and your data directory was just moved.

The reason I want to do the cleaning through the web library interface is because I would like to clean the database before installing (and syncing) zotero on a computer I have, which has very limited disk space.

There's no need for that. You can just set Zotero to download files "as needed" in the Sync pane of the preferences before you sync, and it will only download files that you open (which you can delete again via right-click → Show File if you want). Again, you really want to use the desktop app for any significant work.

sorry to bother you again: I did not find how to delete _locally_ a pdf (from a shared, group library):
I am not syncing attached pdf; I only download them "as needed. I would like to be able to delete them again from my local Zotero storage (without deleting them from the shared library on the web). I tried to right-click on the pdf, but did not see any option that seem to enable the removing of the pdf file locally (my zotero is in French).
How can I remove downloaded pdf _locally_ (while keeping them on the remote, web library)?

thank you