Tcl

PDF Signature Appearance Width and Height

See more PDF Signatures Examples

This example explains how the width and height of the signature appearance rectangle box is determined. Tcl

load ./chilkat.dll

set success 0

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

set pdf [new_CkPdf]

# Load a PDF to be signed.
# The "hello.pdf" is available at https://chilkatsoft.com/hello.pdf
set success [CkPdf_LoadFile $pdf "qa_data/pdf/hello.pdf"]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    exit
}

# Options for signing are specified in JSON.
set json [new_CkJsonObject]

# In most cases, the signingCertificateV2 and signingTime attributes are required.
CkJsonObject_UpdateInt $json "signingCertificateV2" 1
CkJsonObject_UpdateInt $json "signingTime" 1

# Put the signature on page 1, top left
CkJsonObject_UpdateInt $json "page" 1
CkJsonObject_UpdateString $json "appearance.y" "top"
CkJsonObject_UpdateString $json "appearance.x" "left"

# Add some text.
CkJsonObject_UpdateString $json "appearance.text[0]" "Digitally signed by: cert_cn"
CkJsonObject_UpdateString $json "appearance.text[1]" "current_dt"

# Add a built-in SVG graphic to the right.
CkJsonObject_UpdateString $json "appearance.image" "blue-check-mark"
CkJsonObject_UpdateString $json "appearance.imagePlacement" "right"
CkJsonObject_UpdateString $json "appearance.imageOpacity" "100"

# There are 4 ways the width and height of the signature rectangle can be specified.
# 1) The width and height (in points) are both explicitly specified.
#    User space coordinates use "points" where 72 points equals 1 inch.
#    For example (3 inches wide and 1 inch high)
#    The fontScale is automatically chose to fit.  In addition, if a graphic (JPG or built-in SVG) is included,
#    it is automatically scaled such that the text + graphic fit together in the specified rectangle.
#    Note: When both height and width are explicitly specified, the resultant signature appearance rectangle
#    will match one of the dimensions, but the other dimension will be equal or smaller.  This is because the text
#    must be proportionally scaled.
CkJsonObject_UpdateInt $json "appearance.width" [expr 72 * 3]
CkJsonObject_UpdateInt $json "appearance.height" 72

# The signature would have this appearance. In this case, the height is actually less than 1 inch because
# if Chilkat chose a fontScale to fill the height, the resulting text's width would be too long for the desired width. 
# (image:https://example-code.com/images/explicit_width_height.jpg/endImage)

# 2) The width is explicitly specified, but we use the keyword "auto" for height.
#    In this case, the fontScale is chosen to achieve the desired width,
#    and the height will be whatever the result of the chosen font scale.
#    In this example, the width is 4 inches, and the height is "auto".
CkJsonObject_UpdateInt $json "appearance.width" [expr 72 * 4]
CkJsonObject_UpdateString $json "appearance.height" "auto"

# The signature would have this appearance: 
# (image:https://example-code.com/images/explicit_width_auto_height.jpg/endImage)

# 3) The height is explicitly specified, but we use the keyword "auto" for width.
#    In this case, the fontScale is chosen to achieve the desired height,
#    and the width will be whatever the result of the chosen font scale.
#    In this example, the height is 1 inch (72 points) and the width is "auto".
CkJsonObject_UpdateString $json "appearance.width" "auto"
CkJsonObject_UpdateInt $json "appearance.height" 72

# The signature would have this appearance.
# (image:https://example-code.com/images/explicit_height_auto_width.jpg/endImage)

# 4) Finally, we don't need to specify width/height at all.  Instead, we can choose a fontScale
#    and the dimensions of the PDF signature appearance's rectangle will be the result of using the
#    specified fontScale.

set jAppearance [new_CkJsonObject]

CkJsonObject_ObjectOf2 $json "appearance" $jAppearance

CkJsonObject_Delete $jAppearance "width"
CkJsonObject_Delete $jAppearance "height"
CkJsonObject_UpdateString $json "appearance.fontScale" "10.0"

# With fontScale = "10.0"
# (image:https://example-code.com/images/font_scale_10.jpg/endImage)

# Load the signing certificate. (Use your own certificate.)
set cert [new_CkCert]

set success [CkCert_LoadPfxFile $cert "qa_data/pfx/myPdfSigningCert.pfx" "pfx_password"]
if {$success == 0} then {
    puts [CkCert_lastErrorText $cert]
    delete_CkPdf $pdf
    delete_CkJsonObject $json
    delete_CkJsonObject $jAppearance
    delete_CkCert $cert
    exit
}

# Tell the pdf object to use the certificate for signing.
set success [CkPdf_SetSigningCert $pdf $cert]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    delete_CkJsonObject $json
    delete_CkJsonObject $jAppearance
    delete_CkCert $cert
    exit
}

set success [CkPdf_SignPdf $pdf $json "qa_output/hello_signed.pdf"]
if {$success == 0} then {
    puts [CkPdf_lastErrorText $pdf]
    delete_CkPdf $pdf
    delete_CkJsonObject $json
    delete_CkJsonObject $jAppearance
    delete_CkCert $cert
    exit
}

puts "The PDF has been successfully cryptographically signed."

delete_CkPdf $pdf
delete_CkJsonObject $json
delete_CkJsonObject $jAppearance
delete_CkCert $cert