Zig

PDF Signature Page Location

See more PDF Signatures Examples

This example demonstrates how to specify the location of a PDF signature on a page.

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 {};

    // When cryptographically signing a PDF, the signature's appearance can be placed on a specific
    // page in the PDF document, and at a specified location on the page.
    // The 1st page of the PDF document is page number 1 (we don't use 0-based numbering for PDF page numbers).
    // The PDF object has a NumPages property, so we can use it to sign on the last page of the PDF.
    json.updateInt("page", pdf.getNumPages()) catch {};

    // appearance.y and appearance.x JSON properties control the x,y location of the signature.
    // The "appearance.y" can be "top" or "bottom".
    // The "appearance.x" can be "left", "middle", or "right".
    // It is also possible to specify exact PDF location in user space coordinates, which is discussed below.
    json.updateString("appearance.y", "bottom") catch {};
    json.updateString("appearance.x", "middle") catch {};

    // In this example, the fontScale (in combination with the number of appearance text lines and the length of the longest text line),
    // automatically determine the width/height of the signature text box. Any included graphic (JPG image or built-in SVG) is automatically
    // scaled to fit. It is alternatively possible to specify the desired width/height of the signature rectangle.  In that case
    // you would NOT specify a fontScale because Chilkat would automatically chose a font scale to fit the text to the desired rectangle.
    // This example demonstrates how to specify the exact width/height of the PDF signature text box.
    json.updateString("appearance.fontScale", "9.0") catch {};

    json.updateString("appearance.text[0]", "Digitally signed by: cert_cn") catch {};
    json.updateString("appearance.text[1]", "current_dt") catch {};
    json.updateString("appearance.image", "document-accepted") catch {};
    json.updateString("appearance.imagePlacement", "left") catch {};
    json.updateString("appearance.imageOpacity", "100") 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", "pfx_password") 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 here:

    // ----------------------------------------------------------------------------------------------------
    // *** Scroll down for information about specifying the PDF signature x,y location in user space coordinates.
    // ----------------------------------------------------------------------------------------------------

    // (image:https://example-code.com/images/bottom_middle_signature.jpg/endImage)

    // The x,y coordinates of a PDF page are in "user space", called "points", and there are 72 pointes per inch.
    // A PDF page (8.5" x 11") is 612 points wide and 792 points high.
    // The bottom left is at 0,0.    The top right is at 612,792.
    //
    // To specify the location of a signature rectangle, the "appearance.y" is the y coordinate of the top of the signature rectangle,
    // and the "appearance.x" is the x coordinate of the left of the signature rectangle.
    // Therefore, to position the signature rectangle at the exact top/left of the page, we do this:

    json.updateString("appearance.y", "792") catch {};
    json.updateString("appearance.x", "0") catch {};

    json.updateString("appearance.text[0]", "Digitally signed again by: cert_cn") catch {};
    json.updateString("appearance.text[1]", "current_dt") catch {};
    json.updateString("appearance.image", "document-accepted") catch {};
    json.updateString("appearance.imagePlacement", "right") catch {};

    const pdf2 = try chilkat.Pdf.init();
    defer pdf2.deinit();
    try pdf2.loadFile("qa_output/hello_signed.pdf");
    try pdf2.setSigningCert(cert);

    pdf2.signPdf(json, "qa_output/hello_signed2.pdf") catch {
        std.debug.print("{s}\n", .{try pdf2.getLastErrorText(alloc)});
        return;
    };

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

    // Here we have the PDF with the signature just added at the exact top/left.
    // (image:https://example-code.com/images/pdf_signature_top_left.jpg/endImage)
}