There are different ways to calculate a word count in Word. The way the earlier code determines word count is not what a normal English speaker would consider the Word count - it includes punctuation as a word. This code modification uses an alternate method to arrive at a word count and might work better for your documents
Code:
Sub Macro1()
Dim iWords As Double, sFiller As String, arrFiller() As String, i As Integer
sFiller = "I didn't bother to attempt my homework by myself but I asked someone on the internet to do it for me"
arrFiller = Split(sFiller, " ")
iWords = ActiveDocument.Range.ComputeStatistics(wdStatisticWords) 'ActiveDocument.Words.Count
If iWords < 20 Then
For i = 0 To 19 - iWords
ActiveDocument.Range.InsertAfter " " & arrFiller(i)
Next i
End If
End Sub