PDF encryption

Papyra encrypts PDF output with AES-256 using the PDF 2.0 standard security handler (ISO 32000-2, /V 5 /R 6) - the current, non-deprecated encryption scheme. Older schemes (RC4, AES-128) are deliberately not offered.

byte[] pdf = document.RenderAsPdf(new PdfRenderOptions
{
    Standard = PdfStandard.Pdf20,
    Encryption = new PdfEncryption
    {
        UserPassword = "open-me",
        OwnerPassword = "admin-only",
        Permissions = PdfPermissions.Print | PdfPermissions.ExtractForAccessibility,
    },
});

Encryption requires plain PDF 2.0

PDF/A forbids encryption, and Papyra’s default output is PDF/A. Encryption therefore requires Standard = PdfStandard.Pdf20 - the plain (non-archival) PDF 2.0 mode, which carries none of the PDF/A scaffolding (no XMP packet, output intent, or embedded ICC profile; document metadata lives in the Info dictionary, encrypted like everything else).

Any other standard throws at render time, and the bundled analyzer flags the literal-initializer case at compile time as PAPY106, with a code fix that sets the standard for you.

Encryption and Factur-X e-invoicing are mutually exclusive - Factur-X requires PDF/A-3. Plain attachments work under Pdf20 and are encrypted along with the rest of the file.

Passwords

UserPassword	Required to open the document. When null or empty, the document opens without a password, but Permissions still apply.
OwnerPassword	Grants full access regardless of Permissions. When null, the user password also acts as the owner password.

At least one password must be non-empty. Passwords are Unicode-normalized (NFC), UTF-8 encoded, and truncated to 127 bytes per the spec. Full RFC 4013 SASLprep is not applied - everyday passwords (including non-ASCII letters like umlauts) interoperate with mainstream readers, but passwords built from exotic control or format characters may not round-trip against a strictly conforming reader.

Permissions

PdfPermissions is a flags enum mapped to the standard permission bits (ISO 32000-2 Table 22). The default is All.

Flag	Allows
Print	Printing (possibly degraded without PrintHighResolution)
PrintHighResolution	Full-resolution printing
CopyContent	Copying/extracting text and graphics
ExtractForAccessibility	Extraction for accessibility (PDF 2.0 readers always allow this; the bit still matters to older readers)
ModifyContents	Editing document content
Annotate	Adding annotations and filling forms
FillForms	Filling forms even when Annotate is denied
AssembleDocument	Inserting/rotating/deleting pages, creating bookmarks

Permissions restrict readers opened with the user password; the owner password is never restricted. Note that permissions are an instruction to the viewer, not cryptography - a viewer can simply ignore them; only the passwords are cryptographically enforced.

Non-deterministic output

Papyra’s unencrypted output is byte-identical for identical documents. Encrypted output deliberately is not: the file encryption key, salts, and per-string/stream initialization vectors are freshly random on every render, as sound cryptographic practice requires. Rendering the same document twice produces different bytes that decrypt to identical content.

See also

• PDF render options
• PDF/A output - why the archival standards and encryption exclude each other