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Lua Requires Chilkat v9.5.0.85+

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.

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Lua 
local chilkat = require("chilkat")

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

local pdf = chilkat.Pdf.new()

-- Load a PDF to be signed.
-- The "hello.pdf" is available at https://chilkatsoft.com/hello.pdf
local success = pdf:load_file("qa_data/pdf/hello.pdf")
if not success then
    print(pdf.last_error_text)
    return
end

-- Options for signing are specified in JSON.
local json = chilkat.JsonObject.new()

-- In most cases, the signingCertificateV2 and signingTime attributes are required.
json:update_int("signingCertificateV2", 1)
json:update_int("signingTime", 1)

-- Put the signature on page 1, top left
json:update_int("page", 1)
json:update_string("appearance.y", "top")
json:update_string("appearance.x", "left")

-- Use a font scale of 10.0
json:update_string("appearance.fontScale", "10.0")

-- 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:update_string("appearance.text[0]", "Digitally signed by: cert_cn")
json:update_string("appearance.text[1]", "current_dt")
json:update_string("appearance.text[2]", "The crazy brown fox jumps over the lazy dog.")

-- 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

local jpgData = chilkat.BinData.new()
success = jpgData:load_file("qa_data/jpg/university.jpg")
if not success then
    print("Failed to load the JPG image.")
    return
end

success = pdf:set_signature_jpeg(jpgData)
if not success then
    print(pdf.last_error_text)
    return
end

-- Specify that we want to display the JPG image in the center with 30% opacity.
json:update_string("appearance.image", "custom-jpg")
json:update_string("appearance.imagePlacement", "center")
json:update_string("appearance.imageOpacity", "30")

-- Load the signing certificate. (Use your own certificate.)
local cert = chilkat.Cert.new()
success = cert:load_pfx_file("qa_data/pfx/myPdfSigningCert.pfx", "secret")
if not success then
    print(cert.last_error_text)
    return
end

-- Tell the pdf object to use the certificate for signing.
success = pdf:set_signing_cert(cert)
if not success then
    print(pdf.last_error_text)
    return
end

success = pdf:sign_pdf(json, "qa_output/hello_signed.pdf")
if not success then
    print(pdf.last_error_text)
    return
end

print("The PDF has been successfully cryptographically signed.")

-- 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