Is it possible to modify PDF Form Field Names?

The good news: you can change field names in iTextSharp.

You can't actually edit a PDF though. You'd read in an existing PDF, update your field names in memory and then write out your revised PDF. To change a field name call the AcroFields.RenameField method.

Here's a snippet:

PdfReader reader = new PdfReader(PDF_PATH);
using (FileStream fs = new FileStream("Test Out.pdf", FileMode.Create)) {
    PdfStamper stamper = new PdfStamper(reader, fs);
    AcroFields fields = stamper.AcroFields;
    fields.RenameField("oldFieldName", "newFieldName");
    stamper.Close();
}

Now the bad news: there appear to be limitations in the characters you can use in the renamed fields.

I tested the snippet above with your example field name and it didn't work. Remove the periods though and it does work. I'm not sure if there's a workaround but this may be a problem for you,

The full name of an AcroForm field isn't explicitly stored within a field. It's actually derived from a hierarchy of fields, with a dot delimited list of ancestors appearing on the left.

Simply renaming a field from 'topmostSubform[0].Page1[0].Website_Address[0]' to 'WebsiteAddress' is therefore unlikely to produce a correct result.

You'll find section 8.6.2 'Field Dictionaries' of the PDF reference provides a good explanation of how field naming works ;-)

Basically, each field in an AcroForm is define by a dictionary, which may contain certain optional entries pertaining to a field's name.

• Key '/T' specifies the partial name. In your question, 'topmostSubform[0]', 'Page1[0]', and Website_Address[0], all represent partial names.

• Key '/TU' specifies an alternative 'user-friendly' name for fields, which can be used in place of the actual field name for identifying fields in a user interface.

Instead of renaming the field in question, think about adding a /TU entry!

The example below uses ABCpdf to iterate through all the fields in an AcroForm and insert an alternate name into a field based on its partial name.

VBScript:

Set theDoc = CreateObject("ABCpdf7.Doc")
theDoc.Read "myForm.pdf"

Dim theFieldIDs, theList
theFieldIDs = theDoc.GetInfo(theDoc.Root, "Field IDs")
theList = Split(theFieldIDs, ",")

For Each fieldID In theList
    thePartialName = theDoc.GetInfo(fieldID, "/T:text")
    theDoc.SetInfo fieldID, "/TU:text", thePartialName
Next

theDoc.Save "output.pdf"
theDoc.Clear

Changing "/TU:text" to "/T:text" will set a field's partial name.

Examples written in C# and VB.NET of the functions used can be found here: Doc.GetInfo, Doc.SetInfo. See also the documentation on Object Paths.

I had the problem yesterday and after trying out answers in the forum and others but made no headway. My code looked like this.

// Open up the file and read the fields on it.
var pdfReader = new PdfReader(PATH_TO_PDF);
var fs = new FileStream(pdfFilename, FileMode.Create, FileAccess.ReadWrite)
var stamper = new PdfStamper(pdfReader, fs);
var pdfFields = stamper.AcroFields;

//I thought this next line of code I commented out will do it
//pdfFields.RenameField("currentFieldName", "newFieldName");

// It did for some fields, but returned false for others.
// Then I looked at the AcroFields.RenameField method in itextSharp source and noticed some restrictions. You may want to do the same.
//  So I replaced that line  pdfFields.RenameField(currentFieldName, newFieldName); with these 5 lines

AcroFields.Item item = pdfFields.Fields[currentFieldName];
PdfString ss = new PdfString(newFieldName, PdfObject.TEXT_UNICODE);
item.WriteToAll(PdfName.T, ss, AcroFields.Item.WRITE_VALUE | AcroFields.Item.WRITE_MERGED);
item.MarkUsed(pdfFields, AcroFields.Item.WRITE_VALUE);
pdfFields.Fields[newFieldName] = item;

And that did the job