From your description, it's possible a mailmerge would be the way to go, but it's unclear whether the CSV file has headers that repeat every 20 rows and whether you just want the output to all go into the same place in the document (i.e. a new table every 20 rows, one after the other) or whether you want to create replicas of the document with the same content, except for the table data, every 20 rows.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]