Encrypting a PDF ensures only people with the correct password can open it — critical for sensitive documents like tax returns, medical records, or legal agreements. Here is how to encrypt a PDF for free, entirely in your browser.
Encryption scrambles the PDF content using a key derived from the password. Without the correct password, the file appears as unreadable binary data. The encryption used by pdfeditor.onl follows the PDF 1.7 standard (128-bit RC4), compatible with all major PDF readers.
Go to pdfeditor.onl/protect-pdf. No account or installation is required. The encryption engine runs in WebAssembly inside your browser — your file is never transmitted.
Click to upload or drag your PDF into the tool. For large PDFs (100+ MB), processing may take a few seconds depending on your device speed.
Enter a strong password — at least 12 characters combining letters, numbers, and symbols. Avoid simple passwords for sensitive documents.
Tip: Write down or store the password securely before downloading. Encrypted PDFs cannot be opened by anyone without it, including yourself.
Click Encrypt & Download. The resulting PDF requires the password to open in any PDF viewer — Chrome, Adobe Reader, Edge, or any mobile PDF app.
For everyday document protection — tax returns, contracts, confidential reports — 128-bit RC4 is sufficient. For the strongest encryption, use AES-256 (available in Adobe Acrobat or similar tools). That said, the security of any encrypted PDF depends primarily on password strength.
Technically, any encryption can be brute-forced given enough time. A long, random password makes this impractical. Short or common words are vulnerable to dictionary attacks.
Minimally — the overhead of encryption is negligible compared to the original PDF content.