What guidance do you need?
Such a form letter can be printed or saved as PDF from FileMaker just by making the body of the layout large enough to display all the merged text--whether that be a single page or multiple pages.
Thanks for the comment. I think you mean that the text box can be expanded beyond the 8.5 X 11 size and it will adjust in the printing.
And I guess you can see how it would print in the preview. Right ?
That is essentially correct. But be aware that Preview previews all the records in your current found set starting with the first record--which won't be the current record unless the current record is also the first record. In preview mode, you can click the "book" control to move forward and back through preview one page at a time.