you should never open a .bak file in an app (it's technically a sqlite file, but opening it in an sqlite reader will do nothing to help you, so don't bother with that).
Carefully read and follow the instructions here: https://www.zotero.org/support/zotero_data#restoring_from_the_last_automatic_backup
if there are problems, we need you to describe _exactly_ what you've done and the error messages you're getting.
To make sure, try this with a copy of your regular database, not the .bak - i.e. just zotero.sqlite
does that work?
Also, where is the .bak file from that you're trying to upload? In other words, please spend some time describing what's actually going on, what happened so that you're trying to restore from a back-up in the first place etc. The more detail the better. If you find that easier to do in your native language, feel free to write in that.
The file you're uploading appears to be some sort of encoded Windows filesystem log file. I'm not sure if you're getting that from somewhere else or if your filesystem is genuinely corrupted and overwrote the contents of your Zotero database with that — you'd have to provide more details on where exactly you're getting this file, as adamsmith says.
You should, however, see multiple backup files in your Zotero data directory, so you should try the others, looking at the file dates to see when they're from. (If you have your own backup of your Zotero data directory, then you can also use a copy of the database from that.)
The file .bak is from my old database. I have formated my computer and I've forgot to make a backup of my zotero database. I recovery the file .bak that was not rewritten for anything, but the .sqlite was corrupted. I just need to know if my file is still working (it has 6 mb) and if I'm capable to read informations inside it.
That's why I'm looking for a program or app to read it...
(also - it seems odd you'd have your old .bak but not the regular .sqlite file from the same data directory. I don't really see how that could have happened. Even if the .sqlite is/was corrupted, you could still try to fix it with the repair tool. Just out of curiosity - what't the full filename of the .bak file?).
The main zotero.sqlite might have been replaced by an empty one, but there should still be a .damaged version that was saved automatically. Basically, there should be multiple copies of the database in your Zotero data directory that you could try.
I'll try the .damaged one.
I was thinking that the file was not properly recovered, but I don't want to believe in it!
I want to find a way to read this file or to convert it into RDF file...
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Stop focusing on trying to find a program to read the file. Zotero will read its own database, and the repair tool can usually repair a damaged Zotero database. But this file isn't a Zotero database. It does not contain your Zotero data in any way. I can't be more clear on this.
Upgrade Storage
Carefully read and follow the instructions here: https://www.zotero.org/support/zotero_data#restoring_from_the_last_automatic_backup
if there are problems, we need you to describe _exactly_ what you've done and the error messages you're getting.
"Uploaded file does not appear to be an SQLite database. Please upload a copy of zotero.sqlite."
does that work?
Also, where is the .bak file from that you're trying to upload? In other words, please spend some time describing what's actually going on, what happened so that you're trying to restore from a back-up in the first place etc. The more detail the better. If you find that easier to do in your native language, feel free to write in that.
You should, however, see multiple backup files in your Zotero data directory, so you should try the others, looking at the file dates to see when they're from. (If you have your own backup of your Zotero data directory, then you can also use a copy of the database from that.)
That's why I'm looking for a program or app to read it...
I don't have any other backups, just this one.
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I was thinking that the file was not properly recovered, but I don't want to believe in it!
I want to find a way to read this file or to convert it into RDF file...
=/