How to open .C9S files on iOS
To open .C9S files on iOS, if you received a .c9s file by itself, you generally need the whole vault structure; transfer the entire vault to a device where you can open it with Cryptomator, then unlock the vault to access decrypted content.
Step-by-step instructions
- If you received a .c9s file by itself, you generally need the whole vault structure; transfer the entire vault to a device where you can open it with Cryptomator, then unlock the vault to access decrypted content.
Recommended software
- Textastic
- Kodex
- Files app
Alternative methods
- Open .C9S in a browser-based viewer if desktop apps fail.
- Try opening .C9S on iOS with a secondary app to rule out app-specific issues.
- Convert .C9S only with trusted tools when direct opening is not possible.
Common issues
Trying to open a .c9s file directly shows gibberish or fails
.c9s files are encrypted vault components (ciphertext). They are not intended to be opened as documents outside Cryptomator’s vault unlock process.
- Locate the vault folder that contains the .c9s file (the whole vault structure matters).
- Open/unlock the vault in Cryptomator and use the decrypted mounted view to access the original files.
Unlock fails or files look missing after unlocking
This is often caused by using the wrong vault folder, incomplete vault data (only some files were copied), or a mismatch in vault contents due to partial sync/copy.
- Verify you copied/synced the entire vault folder structure, not individual .c9s files.
- Re-open the correct vault location in Cryptomator and try unlocking again.
File associations or MIME type recognition is not working
Some systems won’t know what to do with .c9s, even though the extension is registered for application/vnd.cryptomator.encrypted; desktop environments may require MIME database updates to recognize it.
- Open the vault from within Cryptomator instead of relying on double-clicking a .c9s file.
- On Linux desktops, ensure your MIME database is up to date per the shared MIME-info mechanism used by your environment.
Security note
.c9s files are encrypted data within a Cryptomator vault; the main security risk is accidental data loss from altering, renaming, or moving ciphertext files inside the vault directory. Manage content through Cryptomator’s decrypted view instead.