PDF Sharp - AddPages replaces form fields-CodePudding

I have a couple of .pdf pages (they are filled forms) that i want to join into a single pdf file.

First I create a pdf document that will hold the info. Then I'm opening each pdf file,

var docToImport = PdfReader.Open(pathToPdf, PdfDocumentOpenMode.Import);

And adding the first page of each pdf to the document i'm creating

doc.AddPage(docToImport.Pages[0]);

The code, creates the pdf file and appends the pdf files that i want.

The problem that i'm not being able to solve is:

if the name of the fields are the same, their values will be overwritten by the next page values.

The last page added, overwrites the previous fields (if they share the same name) Tried changing the field names using

   var form = docIntervencoes.AcroForm;
            var fields = form.Fields;
            var fieldNames = fields.Names;

            for (int idx = 0; idx < fieldNames.Length;   idx)
            {
                var fieldName = fieldNames[idx];
                var field = fields[fieldName];
                field.Elements.SetName($"/Type {fieldName}", $"/Type {fieldName}_{currentIntNumber}");

            }

currentIntNumber is just an int that is incremented from pdf to pdf to get a different name for the fields.

But is does not change the field names.

I'm pulling my hair over this. Just wanted to add pages to the pdf, and keep them as they are. Without overwriting field values.

CodePudding user response：

In PDF files the fields have document scope and not page scope. 2 or more fields with the same name on the same page or on different pages are in fact the same field with multiple widgets (visual representations) and all the widgets display the same field value.

The behavior you encountered is normal and there are 2 possible solutions:

You flatten the form fields after each AddPage call. You will no longer have conflicts, but the fields will no longer be editable.
Rename the fields, either in the destination document or in the source page before calling AddPage.

I'm not familiar with PDFSharp API but it seems to me that you are trying to modify the low level PDF COS dictionary of the field object. The SetName in this situation sets a COS name object in the dictionary and it does not set the field name. Also the low level COS key that stores the field name is /T (not /Type) and its value is a COS string object.

I recommend looking for a Name property or a SetName method on the PDF field object in the PDFSharp API as modifying low level COS object can lead to unexpected results.

CodePudding user response：

Follows the solution to the POSTED issue, using the answer from iPDFdev as a guide:

Flatten did not work out. It actually made the fields non editable but they still ended up being overwritten.
Rename the fields was the way to go!

Follows the solution:

var fields = doc.AcroForm.Fields;
var fieldNames = fields.Names;
for (int id = 0; id < fieldNames.Length;   id){
      var fieldName = fieldNames[id];
      var field = fields[fieldName];
       field.Elements.SetString("/T", $"{ newUniqueFieldName}");
}

Using the SetString was the way to actually change the field name and not just the dictionay entry.