Tables have the Columns proberty and are members of the Tables collection. You can refer to them by item number: thisdocument.Tables(i), where i = 1-6, 9.
Then, for each of those, you can refer to the columns: thisdocument.Tables(i).Columns(j) where j = 2-thisdocument.Tables(i).Columns.Count.
I don't think you can set the Alignment property of a column, only of a row, so you'll have to refer to each cell in the column. That is, for a given column, it has a Cells property which in returns a Cells collection:
for each c in thisdocument.Tables(i).Columns(j).Cells
...
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Bob Rashkin