Add Custom Event handler

public bool HasInvalidPaths(PDFXEdit.IPXC_Annotation annot)
{
	uint invalidCount = 0;
	uint GoTo = pxsInst.StrToAtom("GoTo");
	uint GoToR = pxsInst.StrToAtom("GoToR");
	uint Launch = pxsInst.StrToAtom("Launch");
	PDFXEdit.IPXC_ActionsList actions = annot.get_Actions(PDFXEdit.PXC_TriggerType.Trigger_Up);
	for (uint k = 0; k < actions.Count; k++)
	{
		if ((actions[k].Type == GoTo) || (actions[k].Type == GoToR))
		{
			PDFXEdit.IPXC_Action_Goto actionGoTo = (PDFXEdit.IPXC_Action_Goto)actions[k];
			if (actionGoTo.IsValid == false)
			{
				invalidCount++;
			}
			else if (actions[k].Type == GoToR)
			{
				PDFXEdit.IPXC_FileSpec path = actionGoTo.Target;
				if (File.Exists(path.DIPath) == false)
					invalidCount++;
			}

		}
		else if (actions[k].Type == Launch)
		{
			PDFXEdit.IPXC_Action_Launch actionLaunch = (PDFXEdit.IPXC_Action_Launch)actions[k];
			if (actionLaunch.IsValid == false)
			{
				invalidCount++;
			}
			else
			{
				PDFXEdit.IPXC_FileSpec path = actionLaunch.FileSpec;
				if (path == null)
				{
					if (File.Exists(actionLaunch.FileName) == false)
						invalidCount++;
				}
				else
				{
					if (File.Exists(path.DIPath) == false)
						invalidCount++;
				}

			}
		}
	}
	return (invalidCount > 0);
}

//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);
}

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;
			//
			if (pEvent.Code == (int)0x0201) //WM_LBUTTONDOWN
			{
				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 linkAnnotType = Parent.pxsInst.StrToAtom("Link");
					if (annot.Type == linkAnnotType)
					{
						//If there are any invalid paths then we mark event as handled and this will not execute link action
						pEvent.Handled = true;
						if (Parent.HasInvalidPaths(annot) == false)
							pEvent.Handled = false; //Else we go through link
					}
				}

			}
			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)
		{

		}
	}