using (PdfDocument pdfDocument = PdfDocument.Load("example.pdf")) { PdfAcroForm acroForm = pdfDocument.AcroForm.GetAcroForm(); // Now you can manipulate the form fields. PdfTextField textField = acroForm.Fields[0] as PdfTextField; textField.Value = "John Smith"; }In this example, we load a PDF document and obtain its AcroForm using the GetAcroForm method. We then manipulate a form field (in this case, a text field) by setting its value to "John Smith". The PdfAcroForm.GetAcroForm method is part of the PdfiumViewer package library, which is a .NET wrapper around the PDFium library. This library allows you to view and manipulate PDF documents in C# and other .NET languages.