AddCustomSignatureHandler.cs

public partial class CustomEventTarget:
		PDFXEdit.IUIX_ObjImpl,
		IDisposable
{
	//Here we push custom implementation of the PagesView
	public CustomEventTarget(PDFXEdit.IUIX_Obj obj, MainFrm parentForm)
	{
		Obj_ = obj;
		if (Obj_ != null)
			Obj_.PushImpl(this);
		Parent = parentForm;
	}
	~CustomEventTarget()
	{
		Dispose();
	}
	//Disposing of all of the links we made with objects and parent
	public void Dispose()
	{
		Parent = null;
		if (Disposed_)
			return;
		Disposed_ = true;
		if (Obj_ != null)
		{
			Obj_.PopImpl(this);
			System.Runtime.InteropServices.Marshal.ReleaseComObject(Obj_);
			Obj_ = null;
		}
	}

	//Main form - a parent that in our case holds the PDFXEdit control
	public MainFrm Parent = null;
	//Object for which we are implementing the custom event listener
	public PDFXEdit.IUIX_Obj Obj_;
	//Used for single dispose control
	private bool Disposed_ = false;

	// IUIX_ObjImpl
	public PDFXEdit.IUIX_Obj Obj
	{
		get { return this.Obj_; }
	}
	//Getting Y coordinate from event param2
	public static short HiWord(uint dword)
	{
		return (short)(dword >> 16);
	}
	//Getting X coordinate from event param2
	public static short LoWord(uint dword)
	{
		return (short)dword;
	}

	//Event listener that listens for all of the needed events
	public void OnEvent(PDFXEdit.IUIX_Obj pSender, PDFXEdit.IUIX_Event pEvent)
	{
		
		//If the event is not handled then it will be 
		pEvent.Handled = false;
		// In case of the signatures, we will need to handle LMB click and double click
		if ((pEvent.Code == (int)0x0201) //WM_LBUTTONDOWN
			|| (pEvent.Code == (int)0x0203)) //WM_LBUTTONDBLCLK
		{
			PDFXEdit.tagPOINT pt;
			pt.x = LoWord(pEvent.Param2);
			pt.y = HiWord(pEvent.Param2);
			int nHitTestCode = 0;
			PDFXEdit.IPXC_Annotation annot = Parent.pdfCtl.Doc.ActiveView.PagesView.GetAnnotFromPt(ref pt, out nHitTestCode);

			if (annot != null)
			{
				//Getting atom from IPXS_Inst
				uint widgetAnnotType = Parent.pxsInst.StrToAtom("Widget");
				if (annot.Type == widgetAnnotType)
				{
					if (annot.Field != null)
					{
						if (annot.Field.Type == PDFXEdit.PXC_FormFieldType.FFT_Signature)
						{
							Parent.pdfCtl.Doc.CoreDoc.CosDocument.LockDocument();
							bool bIsEmpty = true;
							do
							{
								if (annot.Field.PDFObject == null)
									break;
								PDFXEdit.IPXS_PDFVariant var = annot.Field.PDFObject.Dict_Get("V");
								if (var == null)
									break;
								if (var.Type != PDFXEdit.PXS_PDFVariantType.PVT_Dictionary)
									break;
								bIsEmpty = false;

							} while (false);
							Parent.pdfCtl.Doc.CoreDoc.CosDocument.UnlockDocument();

							if (bIsEmpty == true)
							{
								pEvent.Handled = true;
								//////////////////////////////////////////////////////////////////////
								//Paste your code here
								//////////////////////////////////////////////////////////////////////
							}
						}
					}
				}
			}

		}
		else if (pEvent.Code == (int)PDFXEdit.UIX_EventCodes.e_BeforeDestroy)
		{
			Dispose();
		}
		else if (pEvent.Code == (int)PDFXEdit.UIX_EventCodes.e_Last)
		{
			Dispose();
		}
	}

	public void OnPostEvent(PDFXEdit.IUIX_Obj pSender, PDFXEdit.IUIX_Event pEvent)
	{

	}

	public void OnPreEvent(PDFXEdit.IUIX_Obj pSender, PDFXEdit.IUIX_Event pEvent)
	{

	}
}

//Target that will contain the custom event handler implementation for the given object
public CustomEventTarget myEventTarget = null; //!!!!!!PS: Do not forget to dispose of it (we do it in Form1_FormClosed)!!!!!

private void initilaizeCustomEventListenerToolStripMenuItem_Click(object sender, EventArgs e)
{
	//Creating the drop target and filling it's supported formats
	myEventTarget = new CustomEventTarget(pdfCtl.Doc.ActiveView.PagesView.Obj, this);
}