OwnerPassword

public string OwnerPassword { get; set; }

Document doc = new Document();
DocumentBuilder builder = new DocumentBuilder(doc);

builder.Writeln("Hello world!");

// Extend permissions to allow the editing of annotations.
PdfEncryptionDetails encryptionDetails =
    new PdfEncryptionDetails("password", string.Empty, PdfPermissions.ModifyAnnotations | PdfPermissions.DocumentAssembly);

// Create a "PdfSaveOptions" object that we can pass to the document's "Save" method
// to modify how that method converts the document to .PDF.
PdfSaveOptions saveOptions = new PdfSaveOptions();
// Enable encryption via the "EncryptionDetails" property.
saveOptions.EncryptionDetails = encryptionDetails;

// When we open this document, we will need to provide the password before accessing its contents.
doc.Save(ArtifactsDir + "PdfSaveOptions.EncryptionPermissions.pdf", saveOptions);