使用iTextSharp将图像插入PDF表单

Question

有几篇与此主题相关的文章，但是我能做的是将图像插入PDF文件而不是PDF表单内的字段。

我可以使用iText Sharp成功地将文本插入PDF表单，

该类如下：

public class ProcessForm__EmpApp_En
{
    public static void ProcessForm(SMDEntities _DB, WebApplicationFirstPhase EL)
    {
        string __EA_Form_Template = HostingEnvironment.MapPath("~/Content/BaseFiles/OriginalFormTemplate.pdf");
        string newEAForm = HostingEnvironment.MapPath("~/Content/CandidateForms/EA_" + EL.CandidateKey + ".pdf");

        PdfReader pdfReader = new PdfReader(__EA_Form_Template);
        PdfStamper pdfStamper = new PdfStamper(pdfReader, new FileStream(newEAForm, FileMode.Create));
        AcroFields pdfFormFields = pdfStamper.AcroFields;

        // set form pdfFormFields
        pdfFormFields.SetField("Txt_DC_01", EL.ApplicationDistributionCenter);
        pdfFormFields.SetField("Txt_Edu04_Start_Date", EL.Education4StartDate);
        pdfFormFields.SetField("Txt_Edu04_End_Date", EL.Education4EndDate);
        pdfFormFields.SetField("Txt_Edu04_Address", EL.Education4Address);

        //I have an Image field called "ImageLogo" and I don't know how to insert my logo in it?

    }
}

我进行了很多搜索，发现了一些解决方案，但是它们无法正常工作。他们可能已经过时了吗？例如，我在Stackoverflow上找到了一篇有关类似问题的文章，看来该问题已解决。当我应用相同的更改时，出现错误。

文章链接：iTextSharp Fill Pdf Form Image Field

我的代码（摘自上述文章）

        string pdfTemplate = HostingEnvironment.MapPath("~/Content/CandidateForms/OriginalFormTemplate.pdf");
        var newFile = HostingEnvironment.MapPath("~/Content/CandidateForms/EA_" + EL.CandidateKey + ".pdf");
        var pdfReader = new PdfReader(pdfTemplate);
        var pdfStamper = new PdfStamper(pdfReader, new FileStream(newFile, FileMode.Create));
        var pdfFormFields = pdfStamper.AcroFields;

        string TestImage = HostingEnvironment.MapPath("~/Content/CandidateImages/TestLogo.JPG");
        PushbuttonField ad = pdfFormFields.GetNewPushbuttonFromField("ImageLogo");
        ad.Layout = PushbuttonField.LAYOUT_ICON_ONLY;
        ad.ProportionalIcon = true;
        ad.Image = Image.GetInstance(TestImage);
        pdfFormFields.ReplacePushbuttonField("ImageLogo", ad.Field);

        pdfStamper.Close();

每当我尝试调试代码时，都会出现以下错误：