PowerShell Requires Chilkat v11.7.0+

Replace Text in a Signed PDF (PreserveSignatures)

See more PDF Text Replacement Examples

Applying a text replacement rewrites the page content, which invalidates any digital signature on the PDF. While the PreserveSignatures property is true (the default), "apply" is refused on a signed PDF; "check" only reads and is always allowed. Setting PreserveSignatures to false allows the replacement; the signature field stays in the written PDF but no longer verifies, so the document should be signed again afterwards if a signature is wanted. PowerShell

Add-Type -Path "C:\chilkat\ChilkatDotNet47-x64\ChilkatDotNet47.dll"

$success = $false

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

#  The PDF used in this example is available at invoice_signed.pdf

$pdf = New-Object Chilkat.Pdf
$success = $pdf.LoadFile("qa_data/pdf/invoice_signed.pdf")
if ($success -eq $false) {
    $($pdf.LastErrorText)
    exit
}

$("Signatures: " + $pdf.NumSignatures)

$json = New-Object Chilkat.JsonObject
$json.UpdateString("labels[0].label","Invoice Number:")
$json.UpdateString("labels[0].value","INV-2026-0500")

#  "check" reads only, so it works on a signed PDF.
$jsonOut = New-Object Chilkat.JsonObject
$success = $pdf.TextReplace("check",$json,$jsonOut)
if ($success -eq $false) {
    $($pdf.LastErrorText)
    exit
}

$("check: ok = " + $jsonOut.BoolOf("ok"))

#  "apply" is refused while PreserveSignatures is true (the default).
$success = $pdf.TextReplace("apply",$json,$jsonOut)
if ($success -eq $false) {
    $("apply refused: " + $pdf.LastErrorText)
}

#  Allowing the signature to be broken:
$pdf.PreserveSignatures = $false
$success = $pdf.TextReplace("apply",$json,$jsonOut)
if ($success -eq $false) {
    $($pdf.LastErrorText)
    exit
}

$("applied: " + $jsonOut.BoolOf("applied"))

#  The written PDF is a full rewrite with the replacement.  The signature field is still in the document,
#  but the bytes it signed are gone, so it no longer verifies.
$success = $pdf.WriteFile("qa_output/invoice_reissued_broken_signature.pdf")
if ($success -eq $false) {
    $($pdf.LastErrorText)
    exit
}

$("Signatures after writing: " + $pdf.NumSignatures)
$sigInfo = New-Object Chilkat.JsonObject
$validated = $pdf.VerifySignature(0,$sigInfo)
$("Signature 0 verifies: " + $validated)

#  Sample output:

#  Signatures: 1
#  check: ok = true
#  apply refused: ChilkatLog:
#    TextReplace:
#      DllDate: Nov  7 2026
#      ChilkatVersion: 11.7.0
#      UnlockPrefix: CHLKAT
#      UnlockStatus: 2
#      Architecture: Little Endian; 64-bit
#      Language: Visual C++ 11.0 / x64
#      VerboseLogging: 0
#      replaceTextOp:
#        op: apply
#        The PDF is signed: replacing text rewrites the content and invalidates the signatures (set PreserveSignatures = false to allow it).
#      --replaceTextOp
#      Failed.
#    --TextReplace
#  --ChilkatLog
#  
#  applied: true
#  Signatures after writing: 1
#  Signature 0 verifies: false