Try this:
Function checkIt(strDone As String, docNew As Document) As Boolean
Set docNew = ActiveDocument
With docNew.Content.Find
.Text = strDone
.Execute
checkIt = .Found
End With
End Function
Sub GetSpellingErrors()
Dim docThis As Document, docNew As Document
Dim iErrorCnt As Integer
Dim iCount As Integer
Set docThis = ActiveDocument
Set docNew = Documents.Add
With docThis
iErrorCnt = .SpellingErrors.Count
For iCount = 1 To iErrorCnt
If Not checkIt(.SpellingErrors(iCount), docNew) Then
Selection.TypeText Text:=.SpellingErrors(iCount)
Selection.TypeParagraph
End If
Next iCount
End With
End Sub