Searching for Text in Header Section of A Word Document

You're probably trying to search in the wrong section/headertype. You could try this code:

Dim rng As Range
Dim intSecCount As Integer
Dim intHFType As Integer
intSecCount = ActiveDocument.Sections.Count
For intSection = 1 To intSecCount
    With ActiveDocument.Sections(intSection)
        For intHFType = 1 To 3
            Set rng = ActiveDocument.Sections(1).Headers(intHFType).Range
            rng.Find.Execute findtext:="This is the text to find", Forward:=True
            If rng.Find.Found = True Then
                Debug.Print "Match" 
            End If
        Next intHFType
    End With
Next intSection

I found the answer on this site and it's a lot more complex than initially thought: http://word.mvps.org/faqs/customization/ReplaceAnywhere.htm

The following code is from the site above, in addition to searching the entire document it includes text replace functionality:

Public Sub FindReplaceAnywhere()
    Dim rngStory As Word.Range
    Dim pFindTxt As String
    Dim pReplaceTxt As String
    Dim lngJunk As Long
    Dim oShp As Shape

    pFindTxt = InputBox("Enter the text that you want to find.", "FIND" )

    If pFindTxt = "" Then
        MsgBox "Cancelled by User"
        Exit Sub
    End If

    TryAgain:
        pReplaceTxt = InputBox( "Enter the replacement." , "REPLACE" )

        If pReplaceTxt = "" Then
            If MsgBox( "Do you just want to delete the found text?", vbYesNoCancel) = vbNo Then
                GoTo TryAgain
            ElseIf vbCancel Then
                MsgBox "Cancelled by User."
            Exit Sub
        End If
    End If

    'Fix the skipped blank Header/Footer problem
    lngJunk = ActiveDocument.Sections( 1 ).Headers( 1 ).Range.StoryType

    'Iterate through all story types in the current document
    For Each rngStory In ActiveDocument.StoryRanges

        'Iterate through all linked stories
        Do
            SearchAndReplaceInStory rngStory, pFindTxt, pReplaceTxt
            On Error Resume Next
            Select Case rngStory.StoryType
                Case 6 , 7 , 8 , 9 , 10 , 11
                    If rngStory.ShapeRange.Count > 0 Then
                        For Each oShp In rngStory.ShapeRange
                            If oShp.TextFrame.HasText Then
                                SearchAndReplaceInStory oShp.TextFrame.TextRange, pFindTxt, pReplaceTxt
                            End If
                        Next
                    End If
                Case Else
                    'Do Nothing
                End Select
                On Error GoTo 0

                'Get next linked story (if any)
                Set rngStory = rngStory.NextStoryRange
            Loop Until rngStory Is Nothing
        Next
End Sub

Public Sub SearchAndReplaceInStory(ByVal rngStory As Word.Range, ByVal strSearch As String , ByVal strReplace As String)
    With rngStory.Find
        .ClearFormatting
        .Replacement.ClearFormatting
        .Text = strSearch
        .Replacement.Text = strReplace
        .Wrap = wdFindContinue
        .Execute Replace:=wdReplaceAll
    End With
End Sub