Zig

PDF Sign Unsigned Signature Field

See more PDF Signatures Examples

Demonstrates how to sign a PDF's unsigned signature field.

Note: This example requires Chilkat v9.5.0.85 or greater.

Zig

const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    const pdf = try chilkat.Pdf.init();
    defer pdf.deinit();

    // Load a PDF containing an unsigned signature field.
    pdf.loadFile("qa_data/pdf/unsigned_sig_field/due_diligence.pdf") catch {
        std.debug.print("{s}\n", .{try pdf.getLastErrorText(alloc)});
        return;
    };

    // A PDF with an unsigned signature field appears in Adobe Acrobat as shown below.
    // (When the mouse pointer is hovered over the field, a tooltip will likely show a message
    // such as "Unsigned signature field (Click to sign)".
    // This example code will automatically find the unsigned signature field,
    // and signs using your certificate.  It automatically sizes the text to the space alotted
    // for the signature.
    // (image:https://example-code.com/images/unsignedSigField.jpg/endImage)

    // Options for signing are specified in JSON.
    const json = try chilkat.JsonObject.init();
    defer json.deinit();

    // In most cases, the signingCertificateV2 and signingTime attributes are required.
    json.updateInt("signingCertificateV2", 1) catch {};
    json.updateInt("signingTime", 1) catch {};

    // We don't specify the page or a specific location because Chilkat will automatically
    // find the unsigned signature field and use its location and size and will scale the
    // signatures visual appearance (text + graphics) to the correct size required to fit.
    // We only need to indicate the desire to fill the unsigned signature field.
    json.updateBool("appearance.fillUnsignedSignatureField", true) catch {};

    // Starting in Chilkat v9.5.0.90, if a PDF contains multiple unsigned signature fields,
    // the field to be signed can be chosen by name:
    // To list unsigned signature fields, see this example: List PDF Unsigned Signature Fields
    json.updateString("unsignedSignatureField", "doctor_signature") catch {};

    // Note: If the PDF document contains multiple unsigned signature fields, Chilkat will
    // sign the 1st one found.

    // In this example, the appearance of the digital signature will contain three lines:
    // 1) The signing certificate's common name
    // 2) The current date/time
    // 3) Some arbitrary text.
    // The keyword "cert_cn" is replaced with the Certificate's Subject Common Name.
    // The keyword "current_dt" is replaced with the current date/time.
    // Any number of appearance text lines can be added.
    json.updateString("appearance.text[0]", "Digitally signed by: cert_cn") catch {};
    json.updateString("appearance.text[1]", "current_dt") catch {};
    json.updateString("appearance.text[2]", "The crazy brown fox jumps over the lazy dog.") catch {};

    // This signature will include one of the built-in SVG graphics (green-check-grey-circle).
    json.updateString("appearance.image", "green-check-grey-circle") catch {};
    json.updateString("appearance.imagePlacement", "left") catch {};

    // Load the signing certificate. (Use your own certificate.)
    const cert = try chilkat.Cert.init();
    defer cert.deinit();
    cert.loadPfxFile("qa_data/pfx/myPdfSigningCert.pfx", "secret") catch {
        std.debug.print("{s}\n", .{try cert.getLastErrorText(alloc)});
        return;
    };

    // Tell the pdf object to use the certificate for signing.
    pdf.setSigningCert(cert) catch {
        std.debug.print("{s}\n", .{try pdf.getLastErrorText(alloc)});
        return;
    };

    pdf.signPdf(json, "qa_output/due_diligence_signed.pdf") catch {
        std.debug.print("{s}\n", .{try pdf.getLastErrorText(alloc)});
        return;
    };

    std.debug.print("The PDF has been successfully cryptographically signed.\n", .{});

    // The appearance of the signature appears in Adobe Acrobat as shown below.
    // (image:https://example-code.com/images/signature3.jpg/endImage)
}