Fill one copy of a PDF form for every row of a spreadsheet. Fill a form for every row of a CSV (csv_text or csv_url, up to 1000 rows). mapping is {column: field_id}; omit it to use the suggested mapping. If mapping is omitted, suggest_mapping runs first and is billed as one context fill. Batches up to 50 rows finish before this returns; larger ones keep running, poll get_batch. Each row is billed as one fill. retention (ephemeral or account_default) is accepted but changes nothing: the form keeps the setting it was created with.