You are overcomplicating this. To bookmark the values in Column 3 with the names from Column 4: ....(see also attached)
Code:
Sub Mcr_Set_Bookmarks()
Dim BKMkName As String
Dim BkmkRange As Range
Dim oCell As Range
Dim rV As Integer
For rV = 2 To ActiveDocument.Tables(1).Rows.Count
Set oCell = ActiveDocument.Tables(1).Cell(rV, 4).Range
oCell.End = oCell.End - 1 'Omit cell end character
BKMkName = oCell.Text
Set BkmkRange = ActiveDocument.Tables(1).Cell(rV, 3).Range
BkmkRange.End = BkmkRange.End - 1 'Omit cell end character
'Add the bookmark to the cell content range
ActiveDocument.Bookmarks.Add Range:=BkmkRange, Name:=BKMkName
Next rV
Set oCell = Nothing
Set BkmkRange = Nothing
End Sub