How to show an image at a text field position?

I have a PDF document which has AcroForm text fields. Now I want to insert a signature image in one of the those fields. I want to place an image on top of the text field position and resize the text field to match the image size.

This is the code I tried to replace the text field with an image image:

I find the text field by its field name:

String position = null;
ListFieldPosition> fieldPositons = form.getFieldPositions("50106");
for (FieldPosition position :fieldPositons) {
    this.position = position.position;
}

This is how I try to set the image on that position:

Image image = Image.getInstance("ImageFileName");
Float dimensions = position.split("x");
image.setAbsolutePosition(dimensions[0], dimensions[1]);
content.addImage(image);

Based on the given image width and height, I need to change the width and height of the text field.

Posted on StackOverflow on Nov 8, 2015 by Naveenkumar Chinnakalappa

It is never a good idea to change the dimensions of an AcroField as all the content in a PDF is added at absolute positions. When you change the dimension of a field, you risk that it will overlap with other content.

Hence, your best option is to adapt the size of the image to the size of the AcroField. As you already indicated, you can get the field position like this:

AcroFields.FieldPosition f = form.GetFieldPositions("50106")[0];

Note that it's not a good idea to make this a string. You can use the FieldPosition object like this:

int page = f.page;
Rectangle rect = f.position;

You can scale and position the image like this:

Image image = Image.getInstance("ImageFileName");
image.ScaleToFit(rect.Width, rect.Height);
image.SetAbsolutePosition(rect.Left, rect.Bottom);

The ScaleToFit() method will scale the image in such a way that it will fit the dimensions of the form field, respecting the original aspect ratio of the image (you don't want to add a stretched image).

You need to page variable to add the image to the correct page:

PdfContentByte canvas = stamper.GetOverContent(page);
canvas.AddImage(image);

Important:

If you add the image as described above, you need to remove the field (this happens automatically if you flatten the form).
If the form field is a button, then you shouldn't use the above code. Instead you should replace the icon of the button. This is described in my answer to the question How to change the icon of a push button field? This answer explains the standard way to do what you're trying to do, but it requires that the field where you want to add the image is a button field (and based on your question, it seems that it's a text field).