Not tested and no error checking
Private Sub CommandButton1_Click()
Dim range As range
Dim i As Long
Dim TargetList As Variant
'No quotes around strings, and separated by commas
TargetList = Split (TextBox1.Caption, ",") '<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
For i = LBound(TargetList) To UBound(TargetList)
Set range = ActiveDocument.range
With range.Find
.Text = TargetList(i)
.Format = True
.MatchCase = True
.MatchWholeWord = False
.MatchWildcards = False
.MatchSoundsLike = False
.MatchAllWordForms = False
Do While .Execute(Forward:=True) = True
range.HighlightColorIndex = wdYellow
Loop
End With
Next
End Sub