PDF privacy: what your documents reveal and how to protect them

PDFs often carry more than the words on the page. Before you send a contract, a medical letter or a set of bank statements, it is worth knowing what else might be inside, how protection actually works, and what happens to your file when you use an online tool.

Metadata: the details behind the document

Most PDFs record information such as the author’s name (often taken from the computer’s user account), the software that created the file, creation and modification dates, and sometimes the original file name or company. In most PDF readers you can see this under File › Properties. It is usually harmless, but it can reveal who drafted a document or that it was produced from a template.

Hidden content you might not expect

• Earlier versions. PDFs can be saved by appending changes, leaving old content inside the file.
• Cropped areas. Cropping hides parts of a page from view but usually leaves them in the file.
• Comments and form data. Notes in collapsed pop-ups, hidden layers and form fields can contain text that isn’t visible on the printed page.
• Attachments. PDFs can embed whole other files.

Fake redaction: the classic mistake

Drawing a black rectangle over text does not remove the text. It is still there underneath and can often be copied, searched or revealed by deleting the rectangle. There are well-publicised cases of court filings and government reports leaking “redacted” names this way.

Real redaction deletes the underlying text and image data and then marks the area. It needs a dedicated redaction feature in desktop PDF software. If you can’t redact properly, a safe workaround for a few pages is to remove the information in the source document and re-export, or to remove whole pages with Delete Pages, which rebuilds the file without them.

How PDF passwords work

PDFs support two kinds of password:

• The open (user) password encrypts the document. Without it, the content can’t be read. This is real protection, as strong as the password and the encryption method.
• The permissions (owner) password sets restrictions such as “no printing” or “no copying”. The file still opens without it. These restrictions are honoured by mainstream readers but are not enforced by encryption, so treat them as a request rather than a lock.

The encryption method matters too. Older PDFs used 40-bit or 128-bit RC4, which is considered weak today. Modern software, including our Protect PDF tool, uses AES-256. Whatever the method, a short or guessable password undermines it: use at least 12 characters, or several unrelated words, and send the password by a different route from the file.

Uploading versus processing in your browser

Most online PDF services work by uploading your file to their servers, processing it there and letting you download the result. Reputable services delete files after a period, but your document still travels across the internet and sits on someone else’s computer for a while, and you are trusting their security and retention policies.

Browser-based processing works differently. The website sends your browser the software, and your file is processed on your own device without being transmitted. PDF365’s live tools work this way. You don’t need to take that on trust: open your browser’s developer tools, go to the Network tab and watch while you process a file. You will see the tool’s code load, but not your document going out.

A pre-send checklist for sensitive PDFs

1. Check File › Properties for names or details you don’t want to share.
2. Look for comments, attachments and form fields; flatten forms you have finished.
3. Never rely on black boxes to hide information.
4. Remove pages that aren’t needed rather than hiding them.
5. If the file is confidential, encrypt it with a strong password and send the password separately.