You can use AddField method to add the form field at any location on a PDF page. If you want to add a field in the footer then make sure to specify the location coordinates which lie in the footer area. For example, the following code snippet adds the text field in the footer area:
//create a FormEditor object and add a new field
Aspose.Pdf.Kit.FormEditor formEditor = new FormEditor(“input.pdf”, “output.pdf”);
formEditor.AddField(FieldType.Text, “fieldname”, 1, 100, 20, 200, 40);
For further details on working with form fields, you can check the help topics on this link.
I hope this helps. If you have any further questions, please do let us know.