PDF Security Basics: Passwords, Encryption, Watermarks and Redaction
PDFs carry contracts, IDs, payslips, and medical letters, so it's worth knowing which protections actually protect and which only look like they do. This guide covers the main options and the mistakes that most often expose information.
Open passwords and encryption
An open password (sometimes called a user password) encrypts the document. Without the password, the contents can't be read, by a person or by software. This is the strongest protection a PDF offers, and it's what Protect PDF on Maher PDF applies, using AES-256 encryption.
Two points follow from how encryption works:
- The password is the security. AES-256 is strong, but a password like "1234" or the company name can be guessed. Use a long passphrase of several unrelated words, or a random password from a password manager.
- There is no recovery. If the password is lost, the content is lost. Maher PDF never sees your password, so nobody here can reset it. Keep an unprotected original in a secure place if you might need it.
Permission restrictions are weaker
Some PDFs open without a password but say they can't be printed or copied. These "permission" settings depend on the PDF reader honouring them, and many tools ignore them. Treat them as a polite request, not protection. If content must stay private, use an open password.
Sharing a protected PDF safely
- Send the password through a different channel from the file: the file by email, the password by phone call or text message.
- Don't put the password in the email subject or file name.
- Agree on a password format with frequent recipients so you don't need to send it every time, but don't reuse it everywhere.
- When the recipient no longer needs protection, they can remove it with Unlock PDF using the password.
Watermarks: a label, not a lock
A watermark such as CONFIDENTIAL or DRAFT tells readers how to treat a document and discourages a draft from being used as final. Add watermark places one across every page. But anyone with editing software can remove or cover a text watermark, so it doesn't stop copying. Combine it with encryption when privacy matters.
Whiteout and cropping are not redaction
This is the most common and most serious mistake. Drawing a white or black box over text, or cropping the page so the text is outside the visible area, changes what you see, but the original text often remains in the file. It can be revealed by copying the text, by removing the box, or by resetting the crop.
On Maher PDF, the Whiteout tool in Edit PDF and Crop PDF are layout tools. Don't use them to remove confidential information. For real redaction, use software with a dedicated redaction feature that removes the underlying content, and check the result by searching for the removed text.
A practical alternative for simple cases: convert the page to an image (for example with PDF to JPG), cover the information on the image, and convert back. Because the page is now a picture, there is no hidden text underneath. Check that no other copy of the original is attached.
Metadata and hidden content
PDFs can contain the author's name, the software used, comments, attachments, and earlier revisions. Before publishing a document widely, open its properties in a PDF reader and check what's there.
Where your files go matters
Uploading a sensitive document to an online service means trusting that service with it. Maher PDF's tools run inside your browser tab, so files are processed on your device rather than uploaded. Read the Privacy Policy for the exact behaviour, including the optional OCR download.
Quick reference
| Goal | Use | Avoid relying on |
|---|---|---|
| Only certain people can read it | Open password (Protect PDF) | Permission restrictions |
| Mark a document as draft or confidential | Watermark | Watermark as protection |
| Remove confidential details | Dedicated redaction, or flattening to images | Whiteout, boxes, cropping |