Sometimes you have to send a copy of your ID card or a supporting document: for a rental, a banking procedure, a registration. Once that document is gone, how do you stop it being used for something else? That is exactly what a watermark is for.
What is a watermark?
It is a semi-transparent text added on top of your document. It states who you are sending it to and why — for example "Given to such-and-such organisation for a rental application". The document stays perfectly readable, but its purpose becomes clear to everyone.
What it really does
By showing the recipient and the reason directly on the copy, the watermark discourages any reuse: whoever receives it can see it was given for a specific case. A watermarked document is far harder to misuse to open an account or sign up for a service in your name.
What a watermark does not do
Let us be honest: a watermark discourages, it does not technically prevent a copy. Once the document is sent, it no longer depends on you. It is a common-sense protection, not a safe — but it clearly reduces the risk of misuse.
How to use it in Mon Écrin
From the Android app, open a photo or a PDF, choose "Watermark before sharing", enter the recipient and the purpose, then send. Everything happens on your phone: the watermarked document is created locally and never leaves your device until you decide to share it.