AES-256 only
PdfEditorOnlineFree uses secure modern AES-256 encryption. There is no weaker compatibility mode or silent fallback when a viewer cannot handle modern encryption.
Private security tool
Protect a PDF with verified AES-256.
Protect a PDF in your browser with separate open and owner passwords plus viewer permissions for printing, copying, editing, annotation, and forms. The tool verifies correct and deliberately wrong passwords before offering the encrypted PDF for download. Permission flags depend on the receiving viewer, do not replace a strong open password, and may affect signatures or specialized PDF features.
Source and verification
Choose the PDF to protect
One existing, unprotected PDF is inspected and encrypted on this device. The original file is never overwritten.
PDF bytes stay on this device
The source, passwords, encrypted output, and reopen checks stay on this device. The file is not sent to an upload endpoint, the original remains untouched, and passwords are cleared from the form after a successful result.
Strong defaults, explicit limits
Encryption strength and viewer restrictions are different controls.
AES-256 protects the document contents with the passwords. Printing, copying, form, annotation, assembly, and editing flags tell conforming viewers what an open-password user may do.
Open and owner passwords
The open password reads the file with selected restrictions. The separate owner password permits unrestricted access in conforming readers and is required so restrictions are not silently undermined.
Permissions are not DRM
PDF permission flags depend on viewer cooperation. Software that intentionally ignores those flags may still copy or modify content after it has legitimately opened the document.
Reopened before download
The internal adapter checks the encryption dictionary, selected permissions, user password, owner password, and a deliberately invalid password before returning the output.
Password compatibility
Use a long secret you can reproduce exactly.
12 characters is the required minimum
Mix character types or use a long generated passphrase. PdfEditorOnlineFree blocks shorter, commonly guessed, and heavily repeated passwords; the strength meter remains guidance, not a guarantee against guessing.
AES-256 passwords are limited to 127 UTF-8 bytes
Use printable ASCII in this release because current viewers disagree on non-ASCII password handling. PdfEditorOnlineFree rejects those passwords instead of producing a file that may not reopen elsewhere.
Lost passwords cannot be recovered
PdfEditorOnlineFree does not store passwords, recovery keys, or document copies. Save both secrets in a trusted password manager before sharing the encrypted PDF.
Test common viewers before wide distribution
Current Chromium, Adobe Acrobat/Reader, macOS Preview, and mobile PDF apps generally open AES-256 files, but permission handling can vary. PdfEditorOnlineFree reports the encryption and permission checks rather than weakening protection for compatibility.
Continue your workflow
Related tools
These available PdfEditorOnlineFree tools are connected to encrypt pdf by the tool catalog.