C# Requires Chilkat v11.7.0+

PDF Placeholders Without a Value: Error, Blank or Keep

See more PDF Text Replacement Examples

Demonstrates the "unusedPlaceholders" option, which decides what happens to a placeholder found on the page that has no value in "placeholders": "error" (the default) makes it a problem with the reason unusedPlaceholder, so nothing is applied; "blank" replaces it with nothing; "keep" leaves it on the page as it is. C#

bool 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_template.pdf

Chilkat.Pdf pdf = new Chilkat.Pdf();
success = pdf.LoadFile("qa_data/pdf/invoice_template.pdf");
if (success == false) {
    Debug.WriteLine(pdf.LastErrorText);
    return;
}

//  Values for every placeholder except {{po}} (the purchase order number, which this customer has none of).
Chilkat.JsonObject json = new Chilkat.JsonObject();
json.UpdateString("placeholders.customer","Acme Corp");
json.UpdateString("placeholders.date","2026-10-18");
json.UpdateString("placeholders.qty1","2");
json.UpdateString("placeholders.desc1","Cordless drill, 18 V");
json.UpdateString("placeholders.price1","$460.00");
json.UpdateString("placeholders.amount1","$920.00");
json.UpdateString("placeholders.qty2","6");
json.UpdateString("placeholders.desc2","Galvanized hinge, 4 inch");
json.UpdateString("placeholders.price2","$12.50");
json.UpdateString("placeholders.amount2","$75.00");
json.UpdateString("placeholders.subtotal","$995.00");
json.UpdateString("placeholders.taxRate","7.35%");
json.UpdateString("placeholders.tax","$73.13");
json.UpdateString("placeholders.total","$1,068.13");

Chilkat.JsonObject jsonOut = new Chilkat.JsonObject();

//  The default, "error": the unfilled {{po}} is a problem and nothing would be applied.
success = pdf.TextReplace("check",json,jsonOut);
if (success == false) {
    Debug.WriteLine(pdf.LastErrorText);
    return;
}

Debug.WriteLine("error (default): ok = " + Convert.ToString(jsonOut.BoolOf("ok")) + ", problem: " + jsonOut.StringOf("problems[0].field") + " " + jsonOut.StringOf("problems[0].reason"));

//  "keep": {{po}} stays on the page, literally.
json.UpdateString("unusedPlaceholders","keep");
success = pdf.TextReplace("check",json,jsonOut);
if (success == false) {
    Debug.WriteLine(pdf.LastErrorText);
    return;
}

Debug.WriteLine("keep: ok = " + Convert.ToString(jsonOut.BoolOf("ok")));

//  "blank": {{po}} is replaced by nothing, leaving "PO Number:" with an empty value.
json.UpdateString("unusedPlaceholders","blank");
success = pdf.TextReplace("apply",json,jsonOut);
if (success == false) {
    Debug.WriteLine(pdf.LastErrorText);
    return;
}

Debug.WriteLine("blank: applied = " + Convert.ToString(jsonOut.BoolOf("applied")));

success = pdf.WriteFile("qa_output/invoice_no_po.pdf");
if (success == false) {
    Debug.WriteLine(pdf.LastErrorText);
    return;
}

//  Sample output:

//  error (default): ok = false, problem: po unusedPlaceholder
//  keep: ok = true
//  blank: applied = true