Filling PDF Fields with values in ASP.NET MVC 5

Question

I want to fill an existing PDF file in my web application (developed in ASP.NET MVC 5). The PDF file has a field named "Text1". In this field I want to write the value "abc". I am currently trying to use PdfSharp for this purpose.

This is how I am currently trying to set a value in a field in the PDF:

var doc = PdfReader.Open(ControllerContext.HttpContext.Server.MapPath("~/Documents/test.pdf"), PdfDocumentOpenMode.Modify);
doc.AcroForm.Fields["Text1"].ReadOnly = false;

That was the preparation.

And after that I tried various things. For example, this:

doc.AcroForm.Elements.SetValue("Text1", "abc");

But this did not work, because string cannot be converted to PdfSharp.Pdf.PdfItem.

I also tried this:

doc.AcroForm.Fields["Text1"].Value = "abc";

Again, I get the same exception as above.

Is there anyway to set the values of the fields of an existing PDF? Does this work with PdfSharp?

Never used PdfSharp, but looking at the source on GitHub, I came up with this: doc.AcroForm.Elements.SetValue("Text1", new PdfString("abc")); It seems there are a variety of classes that derive from PdfItem (PdfString, PdfInteger, etc) - just a guess. — Collen
– Collen, Commented Jan 14, 2021 at 20:32

Ali · Accepted Answer · 2021-01-18 10:42:20Z

4

Ok. I have found the solution.

First, as user Mu-Majid also writes, you have to set the NeedAppearances element to true. This is done as follows:

if (doc.AcroForm.Elements.ContainsKey("/NeedAppearances") == false)
{
    doc.AcroForm.Elements.Add("/NeedAppearances", new PdfBoolean(true));
}
else
{
    doc.AcroForm.Elements.SetValue("/NeedAppearances", new PdfBoolean(true));
}

Then to set the value of a field you have to consider which field type you have. For a simple text field you can set the value as follows:

doc.AcroForm.Fields["Text1"].Value = new PdfString("abc");

The value of a checkbox can be set as follows:

var chckBox = (PdfCheckBoxField)(doc.AcroForm.Fields["chckbx1"]);
chckBox.Checked = true;

As can be seen, you must first explicitly cast the field to the correct type. After that you can set the value.

The same applies to dropdown elements. This is how the value is set for a dropdown element:

var drpDwn = (PdfComboBoxField)(doc.AcroForm.Fields["Dropdown1"]);
drpDwn.Value = new PdfString("3");

In the PDF, the corresponding text for the value "3" then appears in the dropdown.

Many thanks at this point to Mu-Majid for his help.

answered Jan 18, 2021 at 10:42

Ali

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1 Comment

Ali Over a year ago

Also important to mention is that the statement document.AcroForm.Elements.SetValue("/FieldName", new PdfString("yourstring")); did not work for me. The value that was set was not visible in the PDF.

Mu-Majid · Accepted Answer · 2021-01-16 07:01:45Z

2

You have to use PdfString from PDFSharp library like this document.AcroForm.Elements.SetValue("/FieldName", new PdfString("yourstring"));

You also need this if you are attempting to populate PDF form fields, you also need to set the NeedsAppearances element to true. Otherwise, the PDF will "hide" the values on the form.

edited Jan 16, 2021 at 7:01

answered Jan 14, 2021 at 20:44

Mu-Majid

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3 Comments

Ali Over a year ago

I am trying now to do this:

doc.AcroForm.Elements.SetValue("/NeedsAppearances", new PdfBoolean(true));             doc.AcroForm.Elements.SetValue("/Text1", new PdfString("abc"));

But the value is still not visible in the PDF-file. If I try to set the value without a '/' infront of the key I receive a System.ArgumentException: 'A PDF name must start with a slash (/).'. What am I doing wrong?

Mu-Majid Over a year ago

did you check the value of the needAppearance ?

Mu-Majid Over a year ago

something like this : if (doc.AcroForm.Elements.ContainsKey("/NeedAppearances") == false) doc.AcroForm.Elements.Add("/NeedAppearances", new PdfBoolean(true)); else doc.AcroForm.Elements["/NeedAppearances"] = new PdfBoolean(true);

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