Password Protect PDF

Protect a PDF in three steps

1. Choose a PDF up to 20 MiB. If its existing protection requires a password, enter that current password without changing its spaces or spelling.
2. Enter and confirm a new opening password that does not change during compatibility preparation. It must be nonempty and no longer than 127 UTF-8 bytes.
3. Select Protect PDF, wait for opening and document checks, then download protected.pdf. Keep the password separately: this tool has no recovery service.

What the protection does

The new copy uses AES-256 opening-password protection with encrypted metadata. It does not impose printing or editing restrictions, and an authorized reader can remove its encryption.

Case and ordinary leading or trailing spaces matter. The Unicode-3.2 compatibility checks reject passwords that change during mapping or normalization, later-assigned characters and five historical normalization exceptions. This is not unrestricted Unicode support.

An existing current password is passed as entered, without new-password normalization. Re-protection replaces the old opening password and restrictions; it does not prove document ownership or preserve a digital signature.

Before offering a download, the tool checks exact opening behavior, uses a separate reader and compares the reachable document and stream representation. These checks are not a cryptographic audit, universal reader guarantee or promise of byte-identical output.

Examples and useful boundaries

A two-page document produces a protected copy with two pages and an AES-256 result label. The displayed download size is the actual new file size; encryption need not make a PDF smaller.

A current password can be needed to replace existing protection. A PDF that already opens with empty credentials is identified separately, rather than reporting that you entered a wrong password.

The password limit counts prepared UTF-8 bytes, not visible characters. A prepared value of 63 accented é characters and one ASCII character has 127 bytes; 64 of those accented characters have 128 bytes and are rejected rather than truncated.

Compatibility and important limits

Use one ordinary PDF with 1 to 500 pages. Signed, certified, usage-rights and XFA documents, unsupported security handlers, damaged files and over-limit structures are rejected. Ordinary AcroForms, annotations, layers, tags and embedded files are within the preservation profile.

Protection does not sanitize active content, certify authenticity or retain PDF/A, PDF/X or other conformance. The tool does not open document scripts, external resources or attachments, and cannot recover a forgotten password.

The source remains unchanged. The new copy can change serialization, identifiers, version and storage bookkeeping; orphan objects, incremental-edit history, linearization and original bytes are not promised. Portfolio viewer interfaces and universal reader compatibility are not certified.

Output is limited to 40 MiB and the whole Protect operation to 120 seconds; object, descriptor and stream limits also apply. Cancellation, timeout, failed authentication or verification failure leaves no downloadable partial result.

Local file and password handling

The tool does not upload or save your document or passwords. Download is explicit. It releases its temporary resources and clears submitted fields after processing, but cannot promise forensic erasure from browser memory or control copies you keep.