How to highlight text in pdf file programmatically

Question

I am using below mentioned code to highlight text programmaticaly using VB.net But required text is getting selected but doen't get permanently highlighted. Can anybody help me out.
Dim gAvDoc As
Acrobat.CAcroAVDoc 
Dim myhitlist As
Acrobat.CAcroHiliteList 
Dim mypdpage As
Acrobat.CAcroPDPage 
Dim acroPageView As
Acrobat.CAcroAVPageView 
Dim textSelect As
Acrobat.CAcroPDTextSelect 
Dim gPDFPath As
String
Dim gApp AsAcrobat.AcroApp 
gPDFPath =
"C:\Test.pdf"
gApp = CreateObject("AcroExch.App") 
gApp.Show()
gAvDoc = CreateObject("AcroExch.AVDoc") 
gAvDoc.Open(gPDFPath,
"")acroPageView = gAvDoc.GetAVPageView()
acroPageView.GoTo(1)
myhitlist = CreateObject(
"AcroExch.HiliteList")myhitlist.Add(50, 10)
mypdpage = acroPageView.GetPage()
textSelect = mypdpage.CreateWordHilite(myhitlist)
gAvDoc.SetTextSelection(textSelect) 
gAvDoc.ShowTextSelect()
gAvDoc.Close(True) 

Answer 1

Patrick on writting saving code also its not hightlighting the text. Text gets selected but it doen't get highlighted with yellow color...
Dim gAvDoc As
Acrobat.CAcroAVDoc 
Dim myhitlist As
Acrobat.CAcroHiliteList 
Dim mypdpage As
Acrobat.CAcroPDPage 
Dim acroPageView As
Acrobat.CAcroAVPageView 
Dim textSelect As
Acrobat.CAcroPDTextSelect 
Dim gPDFPath As String 
Dim gApp As Acrobat.AcroApp 
Dim mypddoc As Object
gPDFPath ="C:\Test.pdf"
'Initialize Acrobat by creating App object
gApp = CreateObject("AcroExch.App")mypddoc = CreateObject(
"AcroExch.PDDoc") 
gApp.Show()
mypddoc.Open(gPDFPath)
gAvDoc = CreateObject("AcroExch.AVDoc") 
gAvDoc = mypddoc.OpenAVDoc("testing")acroPageView = gAvDoc.GetAVPageView()
acroPageView.GoTo(1)
myhitlist = CreateObject(
"AcroExch.HiliteList")myhitlist.Add(50, 10)
mypdpage = acroPageView.GetPage() 
textSelect = mypdpage.CreateWordHilite(myhitlist)
gAvDoc.SetTextSelection(textSelect)
gAvDoc.ShowTextSelect()
mypddoc.Save(PDSaveFull, gPDFPath)
gAvDoc.Close(True)