Zig

PDF Signature with Background Image (Seal/Stamp/etc.)

See more PDF Signatures Examples

Demonstrates how to sign a PDF with an appearance that includes a background image, such as a seal, stamp, etc.

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 to be signed.
    // The "hello.pdf" is available at https://chilkatsoft.com/hello.pdf
    pdf.loadFile("qa_data/pdf/hello.pdf") catch {
        std.debug.print("{s}\n", .{try pdf.getLastErrorText(alloc)});
        return;
    };

    // 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 {};

    // Put the signature on page 1, top left
    json.updateInt("page", 1) catch {};
    json.updateString("appearance.y", "top") catch {};
    json.updateString("appearance.x", "left") catch {};

    // Use a font scale of 10.0
    json.updateString("appearance.fontScale", "10.0") catch {};

    // 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 {};

    // Load a JPG image to be shown with 30% opacity in the background.
    // (the image must be in the JPG format)
    // The sample university.jpb is available at https://example-code.com/images/university.jpg

    const jpg_data = try chilkat.BinData.init();
    defer jpg_data.deinit();
    jpg_data.loadFile("qa_data/jpg/university.jpg") catch {
        std.debug.print("Failed to load the JPG image.\n", .{});
        return;
    };

    pdf.setSignatureJpeg(jpg_data) catch {
        std.debug.print("{s}\n", .{try pdf.getLastErrorText(alloc)});
        return;
    };

    // Specify that we want to display the JPG image in the center with 30% opacity.
    json.updateString("appearance.image", "custom-jpg") catch {};
    json.updateString("appearance.imagePlacement", "center") catch {};
    json.updateString("appearance.imageOpacity", "30") 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/hello_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.
    // The JPG is automatically scaled to the size of the signature based on the signature's font scale
    // and number of text lines.
    // (image:https://example-code.com/images/signature2.jpg/endImage)
}