Object variable or with block variable not set w/ for loop

I am trying to replace text in a word document from the entries in Excel. When I run the code without the tag for-loop (that means with single tag-value combination) it works as normal. But, I insert the wdDoc.StoryRanges loop inside the outer tags loop I am getting the error

"Object variable or with block variable not set"

despite setting the wdDoc value before the outer loop.

Can any of you please advise.

Thank you very much!

Public Function Test(filepath as String) As Variant
counter = 0

Dim wdApp As Object
Dim wdDoc As Object

Set wdApp = CreateObject("word.application")
wdApp.Visible = True

Set wdDoc = wdApp.Documents.Open(filePath)

For Each tag In tags
  counter = counter + 1
  If Len(tag) > 0 Then
    Dim wdRng As Word.Range
    For Each wdRng In wdDoc.StoryRanges <-- [I am getting the error here]
        With wdRng.Find
            .Text = tag
            .Highlight = True
            With .Replacement
                .Text = values(counter, 1)
                .Highlight = False
            End With
            .Wrap = wdFindContinue
            .Execute Replace:=wdReplaceAll
        End With
        Set wdApp = Nothing: Set wdDoc = Nothing: Set wdRng = Nothing
    Next wdRng
   End If
Next tag
End Function