Compiler error: Sub or function not defined - vba

Question

I am trying to define and call a function from a subroutine. When I run the subroutine, I get "Compiler error: Sub or function not defined". Why is this happening?
The function I am trying to call is th GetImageHeight below, but the same happens with any of the other functions.
I understand that such questions get asked frequently, and the cause is usually the OP doing something stupid. I searched for similar questions, but I still don't get it.
The function below is largely copied from this page
Here the code:
Function FileExists(FilePath As String) As Boolean
 
      
    On Error Resume Next
    If Len(FilePath) > 0 Then
        If Not Dir(FilePath, vbDirectory) = vbNullString Then FileExists = True
    End If
    On Error GoTo 0
 
End Function
 
Function IsValidImageFormat(FilePath As String) As Boolean
 
    Dim imageFormats    As Variant
    Dim i             As Integer
 
    imageFormats = Array(".bmp", ".jpg", ".gif", ".tif", ".png")
 
         For i = LBound(imageFormats) To UBound(imageFormats)
             If InStr(1, UCase(FilePath), UCase(imageFormats(i)), vbTextCompare) > 0 Then
            IsValidImageFormat = True
            Exit Function
        End If
    Next I
 
End Function
Sub DeleteImages()
Dim ThisImage As InlineShape
Dim Height As Double
Dim Width As Double
Dim TotalCount As Integer
Dim Count As Integer
Dim Source As String
Dim ImageHeightPx As Double
Dim ImageWidthPx As Double
Dim ImagePath As String
Dim ImageName As String
Dim FileName As String
ImagePath = "C:\Users\User\Image\"
FileName = Mid(ActiveDocument.Name, 1, InStr(1, ActiveDocument.Name, ".") - 1)
Set myStyle = ActiveDocument.Styles.Add(Name:="Replaced Image", Type:=wdStyleTypeCharacter)
TotalCount = ActiveDocument.InlineShapes.Count
ImageCount = 1
For Each ThisImage In ActiveDocument.InlineShapes
ImageName = FileName & "_IMG_" & Trim(Str(ImageCount))
MsgBox ImageName
ThisImage.Select
Selection.Delete Unit:=wdCharacter, Count:=1
Selection.Style = "Replaced Image"
Selection.TypeText Text:="[[[ " & ImageName & " ]]]"
ImageHeightPx = GetImageHeight(ImagePath & ImageName & ".png")
ImageWidthPx = GetImageWidth(ImagePath & ImageName & ".png")
MsgBox "Height: " & Str(ImageHeightPx)
MsgBox "Width: " & Str(ImageWidthPx)
ImageCount = ImageCount + 1
Next ThisImage
End Sub
Function GetImageHeight(ImagePath As String) As Variant
 
    Dim imgHeight As Integer
    Dim wia As Object
 
    If FileExists(ImagePath) = False Then Exit Function
    If IsValidImageFormat(ImagePath) = False Then Exit Function
 
    On Error Resume Next
    Set wia = CreateObject("WIA.ImageFile")
    If wia Is Nothing Then Exit Function
    On Error GoTo 0
 
    wia.LoadFile ImagePath
 
    imgHeight = wia.Height
 
    Set wia = Nothing
 
    GetImageHeight = imgHeight
 
End Function
 
Function GetImageWidth(ImagePath As String) As Variant
 
    Dim imgWidth As Integer
    Dim wia As Object
 
    If FileExists(ImagePath) = False Then Exit Function
 
    If IsValidImageFormat(ImagePath) = False Then Exit Function
 
    On Error Resume Next
    Set wia = CreateObject("WIA.ImageFile")
    If wia Is Nothing Then Exit Function
    On Error GoTo 0
 
    wia.LoadFile ImagePath
 
    imgWidth = wia.Width
 
    Set wia = Nothing
 
    GetImageWidth = imgWidth
 
End Function
Edits: replaced screenshot with code.

Answer 1

check, you have copied FileExists() and IsValidImageFormat() from source sample into your module.
check, you have selected WIA library for the project
To add WIA 2.0 library:
Click Components from the Project menu (or press Ctrl-T).
Scroll down and select Microsoft Windows Image Acquisition Library
v2.0 by placing a checkmark in front of it. Of the three new controls
that appear on in the Toolbox.