BUG: Set Linked Form Value (#414)

If a form text field is linked to multiple locations in a PDF, PdfFileWriter.updatePageFormFieldValues failed to set the value.

If writer_annot contains a link to a Parent object, the value in that should object should be set.

Closes #398

PyPDF2/pdf.py

@@ -363,6 +363,7 @@ def updatePageFormFieldValues(self, page, fields):
         '''
         Update the form field values for a given page from a fields dictionary.
         Copy field texts and values from fields to page.
+        If the field links to a parent object, add the information to the parent.
 
         :param page: Page reference from PDF writer where the annotations
             and field data will be updated.
@@ -372,11 +373,19 @@ def updatePageFormFieldValues(self, page, fields):
         # Iterate through pages, update field values
         for j in range(0, len(page[PG.ANNOTS])):
             writer_annot = page[PG.ANNOTS][j].getObject()
+            # retrieve parent field values, if present
+            writer_parent_annot = {}  # fallback if it's not there
+            if PG.PARENT in writer_annot:
+                writer_parent_annot = writer_annot[PG.PARENT]
             for field in fields:
                 if writer_annot.get('/T') == field:
                     writer_annot.update({
                         NameObject("/V"): TextStringObject(fields[field])
                     })
+                elif writer_parent_annot.get('/T') == field:
+                    writer_parent_annot.update({
+                        NameObject("/V"): TextStringObject(fields[field])
+                    })
 
     def cloneReaderDocumentRoot(self, reader):
         '''