Share Sensitive Documents Online: Send Only What Is Needed

Additional resource for the lesson “A Guide to Safe Sharing: Protecting Your Sensitive Data” — Online Anonymity course

Sooner or later you will need to share sensitive documents online: a copy of your ID for a rental contract, a signed agreement, an invoice with bank details. Each one leaves your hands and lands somewhere you do not control. This resource shows how to send only what the other side really needs, so that each copy says less about you and is less useful to anyone else.

A. Why this matters

In this course, privacy means deciding what others know about you; anonymity means being able to act without what you do being tied back to who you are. A document is the most direct link there is. An ID copy carries your face, your full name, your date of birth and a document number, all in one file.

Once sent, that file can be forwarded, stored in an inbox, copied into a shared folder or kept long after the reason for sending it has passed. You do not have to imagine anyone acting in bad faith. Ordinary systems simply keep things, and every place that keeps a copy is one more place it could leak from.

What the sources say

The European Commission, explaining the EU’s data protection principles, states that personal data must be “adequate, relevant, and limited to what is necessary for the purpose”. This is data minimisation, and it applies to the organisation asking. It is also a useful question for you to ask: what is necessary here?

The Government of the Netherlands gives unusually concrete advice on ID copies. It says an organisation asking for one “must explain why the copy is necessary”, and that “registering the type of ID provided and the document number is often enough.” Where a copy is needed, it suggests covering details that are not required, such as your photo or national identification number, so that “you do not give away more personal information than strictly necessary.”

The same government explains that only some organisations in the Netherlands, such as banks, notaries and employers, are allowed to copy an ID, and that others may only note the type of document or its number. Rules like these vary by country, so the details where you live may differ.

In the UK, the Information Commissioner’s Office (ICO), the independent data protection authority, reminds the public that an organisation using your data must tell you why, who it will share it with and “how long your data will be kept.”

B. Key concepts: how to share sensitive documents online

Six ideas, from the question to ask first to the checks to make last.

Data minimisation: start with “what do you need?”

Data minimisation means sharing only the data a task really requires. For a document, that might mean sending one page instead of five, an invoice without the bank details of your other customers, or the type and number of your ID rather than a full scan.

Why it matters to you: The cheapest copy to protect is the one you never sent. Asking “what do you need, and why?” is polite, normal, and often changes the answer.

Every copy is a new link

When you send a document, you create a new copy in a system you cannot see: an email server, a shared drive, a customer database. Each copy ties your identity to that place for as long as it is kept, and possibly to whoever can reach it later.

Why it matters to you: This is the anonymity angle. You are not only deciding what one person sees today, but how many places can connect your name, face and numbers in the future.

Covering is not the same as redacting

Redacting means removing information from a document so that it cannot be recovered. Drawing a black rectangle over text, or highlighting it in black, often only covers it. A redaction guide published by the US Court of Federal Claims warns that such a box “merely hides the data”: anyone can copy it, paste it elsewhere and the text underneath appears.

Proper redaction tools delete the content. Adobe describes redaction as “permanently removing visible text and graphics from a document”, and warns that in Acrobat “The items aren’t permanently removed from the document until you save it.”

Why it matters to you: A covered name is still in the file. If you need to remove something, use a tool that redacts, then check the result before you send it.

Hidden data travels with the file

Documents carry information you do not see on the page. As Microsoft puts it, “Document properties, or metadata, include details about your document such as author, subject, and title.” Files can also hold comments and tracked changes.

Office programs and some PDF editors include a check for this: in Word for Windows, Microsoft’s help page puts it under File › Info › Check for Issues › Inspect Document; Adobe Acrobat calls its version Sanitize.

Why it matters to you: A document you want to send without your name, such as feedback or a complaint, can still carry it in its properties. The visible page is not the whole file.

A watermarked copy of your ID

A watermark is a semi-transparent line of text written across a copy, stating who it is for, why and when. It does not hide anything, but it ties the copy to one purpose, so it is harder to reuse for something else.

Two European governments offer free tools for this. The Dutch government’s KopieID app lets you cross out details such as your citizen service number or photo, then adds a watermark: “In this watermark, you state the purpose and date of the copy.” In France, the public employment service describes Filigrane Facile, a government watermarking website, and says it keeps no files.

Why it matters to you: A watermark limits what a stray copy is good for. As France Travail notes, it does not guarantee protection against a determined fraudster: it is one layer, not a shield.

Choosing the channel, and asking how long

The channel is how the document travels: an attachment, a link, an upload form or a portal. Some organisations offer an upload form; using it can keep the file out of email inboxes that are forwarded and kept for years. How a channel protects the file in transit is a security question, covered in the Online Security resource below.

Why it matters to you: The channel decides how many copies exist along the way. Asking how long the copy will be kept is reasonable: in the UK, the ICO says organisations must tell you.

C. A practical example: Gianni’s storage unit

Gianni is 50 and runs a small picture-framing workshop. His business is growing, and he decides to rent a storage unit nearby. The rental company emails him a list: a copy of his ID, proof of address, and a signed form. That same week, a new supplier asks to see how he usually words his terms with clients, so Gianni plans to send an old contract as an example.

His first instinct is speed: he photographs his passport on the workbench, attaches it with a utility bill to a reply email, and opens the old contract to black out the client’s name and address with rectangles in his PDF viewer. It takes ten minutes. Before sending, he remembers a conversation with his accountant, and decides to look again.

What changed when Gianni looked again

He did the exercise in section D, without any sense of alarm:

• He asked the rental company what they needed the ID for. They replied that a copy was required for the contract, but that his photo and signature could be covered.
• He made a new copy with those details covered and a watermark: “Copy for storage unit rental contract only”, with the date.
• He used the company’s upload form rather than email, and asked how long they keep documents. The answer: until the end of the contract.
• In the old contract, he clicked on one of his black rectangles and found he could still select the client’s name beneath it. He redacted the page properly instead, then checked the document properties: the file still listed a former client’s company as the author. He removed it.

Gianni did not refuse to share anything. He still sent an ID copy, a utility bill and a contract. What changed is that each copy now says less, is tied to one purpose, and sits in fewer places.

D. Try it yourself: prepare one minimum copy of an ID document (20 minutes)

Four short steps. If you have nothing to send right now, do it as a dry run and delete the file afterwards. There is no perfect result, only a copy that carries less than before.

Step 1 — Ask what is really needed (4 minutes)

• Think of a recent or upcoming request for your ID: a rental, a new account, a booking.
• Write down what the organisation said it needs, and why. If it did not say, that is a question worth asking.
• Note whether the type and number of your document, or seeing it in person, might be enough instead of a copy.

Step 2 — Make the copy and cover what is not needed (6 minutes)

• Scan or photograph only the side or page that is asked for, on a plain surface with nothing else in the frame.
• Cover details the recipient said it does not need, such as the photo, a signature or a national identification number, using a tool that removes them rather than drawing over them.
• Zoom in on the result: anything still readable is still shared.

Step 3 — Add a purpose-and-date watermark (5 minutes)

• Write a short line: who the copy is for, what it is for, and the date. For example: “Copy for [organisation], [purpose] only, [date]”.
• Two examples of free tools: the Dutch government’s KopieID app on a phone, or the French government’s Filigrane Facile website. Any image or PDF editor that can add text will also work.
• Remember that an online tool is itself a recipient: check what it says about keeping your file before you upload anything.

Step 4 — Check the file and choose the channel (5 minutes)

• Open the final file once more. If it is a PDF or an Office document, look at its properties or run the built-in inspection for hidden data.
• Prefer the organisation’s own upload form or portal, if it has one, to an email attachment or a chat message.
• Ask, or check its privacy information, how long the copy will be kept. Write the answer next to the date you sent it.

One copy you prepared on purpose is worth more than ten sent in a hurry.

Already covered in the Online Security course

Data Encryption: Already On, and Worth Understanding
It explains how encryption protects devices, backups and cloud storage; this resource looks at what a document carries before it leaves your hands, and how many places end up keeping it.

Already covered in the Online Privacy course

Spear Phishing: Why Scam Messages Know So Much About You
It shows how public and leaked details are assembled into convincing scam messages; this resource helps you send fewer of those details in the first place.

E. Videos, articles and further resources

Institutional sources first, then the watermarking tools mentioned in the exercise and the documentation for redaction and hidden data. All in English except the French page.

Institutional sources

European Commission — Principles of the GDPR
The data protection principles, including data minimisation: only what is necessary for the purpose.
https://commission.europa.eu/law/law-topic/data-protection/rules-business-and-organisations/principles-gdpr_en

Information Commissioner’s Office (UK) — Your right to be informed if your personal data is being used
What an organisation must tell you, including why it uses your data and how long it will keep it.
https://ico.org.uk/for-the-public/your-right-to-be-informed-if-your-personal-data-is-being-used/

Government of the Netherlands — How do I prevent a copy of my ID being used for fraudulent activities?
Short, concrete advice: ask why a copy is needed, cover unnecessary details and mark it as a copy.
https://www.government.nl/topics/identity-fraud/question-and-answer/how-do-i-prevent-a-copy-of-my-id-being-used-for-fraudulent-activities

Watermarking tools

Government of the Netherlands — How do I make a secure copy of my ID using the KopieID app?
The government app that crosses out details and adds a purpose-and-date watermark.
https://www.government.nl/topics/identity-fraud/question-and-answer/how-do-i-make-a-secure-copy-of-my-id-with-the-kopieid-app

France Travail — Filigrane Facile : protégez vos documents de candidature contre l’usurpation d’identité
In French: the French government’s free watermarking website, what to write in a watermark and its limits.
https://www.francetravail.fr/candidat/soyez-vigilants/filigrane-facile–un-nouveau-ser.html

Redaction and hidden data

United States Court of Federal Claims — PDF File Redaction Best Practices
Why a black box over text only hides it, and why metadata stays in the file.
https://www.cofc.uscourts.gov/sites/cfc/files/pdf_file_redaction_best_practices.pdf

Adobe Help — Removing sensitive content from PDFs
How redaction removes visible content for good, and how to remove hidden information from a PDF.
https://helpx.adobe.com/ie/acrobat/using/removing-sensitive-content-pdfs.html

Microsoft Support — Remove hidden data and personal information by inspecting documents, presentations, or workbooks
What hidden data an Office file can hold, and how to find and remove it.
https://support.microsoft.com/en-us/office/inspect-your-document-for-hidden-data-or-personal-information-356b7b5d-77af-44fe-a07f-9aa4d085966f

Links checked in November 2026. If an address changes, searching for the title on the organisation’s site usually finds it.

F. The Cyber Welfare Framework: Skills, Awareness, Secure Behaviour

This resource sits on the Secure Behaviour pillar at level FL2 – Beginner: turning a moment of sharing into a few deliberate choices you can repeat.

Skills

• Redacting a document with a tool that removes content, and checking that it worked.
• Finding and clearing the hidden properties of a PDF or Office file.
• Adding a purpose-and-date watermark to a copy of an ID document.

Awareness

• Understanding that each copy you send links your identity to a place you do not control.
• Knowing that a black box drawn over text may only hide it.
• Recognising that a watermark limits what a copy is good for, without making it harmless.

Secure Behaviour

• Asking what is needed, and why, before sending any identity document.
• Sending through the organisation’s own upload channel where one exists.
• Keeping a short note of what you sent, to whom, and how long they keep it.

G. Questions to sit with

• Which documents about you are most likely to be sitting in an inbox you will never see again?
• When someone asks for “a copy of your ID”, what would you need to hear before you felt comfortable sending it?
• Which file on your computer would surprise you most if you opened its properties today?

H. What to do now

The recommendations (R) and security measures (MS) from the Cyber Welfare database that apply most directly here. None of the current codes covers document sharing directly, so the advice below is given without a code.

1. Before you send

• Ask what the other side needs and why; offer the document type and number, or showing it in person, where that could be enough.
• Send ID copies with unnecessary details covered and a watermark stating who it is for, the purpose and the date, using a tool such as KopieID or Filigrane Facile, or any editor you trust.
• Redact with a proper redaction tool, never with shapes or highlighting, and check hidden properties before the file leaves your device.

Minimum commitment: next time someone asks for a copy of your ID, ask what it is for and whether a copy is really needed.

2. After you send

• Keep a short record: what you sent, to whom, when, and how long they said they would keep it.
• Delete your own stray copies once they have served their purpose: in your downloads folder, your sent email or a chat thread.
• When a contract or service ends, you can ask the organisation whether it still holds your documents and when it will delete them.

Minimum commitment: this week, search your sent email for one old scan of an ID document and note who received it.

In short

• When you share sensitive documents online, each copy links your identity to a place you do not control.
• Ask what is needed first: the type and number of an ID are sometimes enough.
• Redact by removing, not covering, and check the hidden properties of the file.
• A watermarked copy, sent through the right channel, carries less and is good for less.

Related resources in this course

• Remove Metadata from Photos Before You Share: A Practical Guide
• Identifying Information Online: Decide What You Share, With Whom
• How to Prevent Doxxing: Spot the Signs, Reduce Your Exposure

Discover more companion resources from the online courses of the Protect Your Digital Privacy programme.