What Is PDF Encryption? How Does AES-256 Work?
We explain what encryption really means and how AES-256-GCM works to keep your documents truly safe.
What exactly is encryption?
Encryption is the process of transforming a document into a form that only people with the correct key can read. When a document is in plain text anyone can open it; once encrypted, the content turns into a meaningless pile of data.
The goal of PDF encryption is to protect the content even if the file ends up in the wrong hands. Even if a contract you send as an email attachment reaches the wrong person, it cannot be opened without the password.
Why is AES-256 the standard?
AES (Advanced Encryption Standard) is an encryption algorithm used worldwide by banks, governments and security agencies. Its 256-bit key length makes it practically impossible to break with brute-force attacks.
Trying every possible combination of a 256-bit key would take today's fastest computers many times longer than the age of the universe. That's why AES-256 is the gold standard for sensitive documents.
What does GCM mode do?
AES-256-GCM protects not only confidentiality but also integrity. GCM (Galois/Counter Mode) adds an authentication tag to the encrypted data.
As a result, even the smallest change to the file makes decryption fail. So if someone tampers with your file it gets noticed — you won't silently receive a corrupted document.
PBKDF2 and password security
The password a user picks is usually short and predictable. PBKDF2 runs that password through 600,000 rounds of processing to turn it into a strong encryption key.
This slowdown is intentional: when an attacker wants to try millions of passwords, every attempt has to run those 600,000 rounds. That makes brute-force attacks economically pointless.
In-browser encryption with FluoLock™
FluoPDF's FluoLock™ feature performs the entire encryption in your browser. Your password is never sent to a server — it never leaves your device.
That means you don't have to trust the server. The document is locked on your device and opened on your device. If you forget your password the file cannot be recovered; that's the price of real security.