Along with Paul's corrections, I would also expect problems with a single line of VBA growing beyond limits. You can reduce the likelihood of that being an issue by simplifying the quote marks and concatenating chunks into separate lines.
Code:
Sub FillerWords()
' Highlights filler words
Dim i As Long, sList As String, TargetList() As String
sList = "admit|all off|as being|as to whether|as yet|care about|go on|grateful every day|if you need to|"
sList = sList & "if you want|if you wish|if you would like to|I might add|in terms of|in my opinion|"
sList = sList & "in spite of that fact that|in the event of|in the event that|in the process of|it seems like|"
sList = sList & "made it to|pick out|pick up on|play up|point out|put off|put together|really|spend|take action to|"
sList = sList & "takes up|taking up|talk about|the most important thing is to|the reason|time and again|took up|"
sList = sList & "try to figure out|went back over|when it comes to|which is|who is|will be different|you can|"
sList = sList & "you're going to|you're going to have|you're going to need to|in general|mostly|sort of|virtually|"
sList = sList & "often|I think|absolutely|definitely|very|totally|literally|just|ironically|truly|actually|basically|"
sList = sList & "to know|I see|I feel|I hear|I can feel|almost|all of|factor|for all intents and purposes|for the most part|"
sList = sList & "for the purpose of|harder than it has to be|individual|initial|on a regular basis|the first step is to|time and time again|with reference to"
TargetList = Split(sList, "|")
Options.DefaultHighlightColorIndex = wdPink
With ActiveDocument.Content.Find
.MatchCase = False
.MatchWholeWord = True
.MatchWildcards = False
.MatchSoundsLike = False
.MatchAllWordForms = False
.Wrap = wdFindContinue
.ClearFormatting
.Replacement.ClearFormatting
.Replacement.Highlight = True
For i = LBound(TargetList) To UBound(TargetList)
.Text = TargetList(i)
.Execute Replace:=wdReplaceAll
Next
End With
End Sub