Is it possible from FileMaker to print a portrait-formatted layout that extends to the full legal sized page? If so, how? If not from Filemaker, are there other ways to do this? Thanks.

Yes, It is possible, but depends also on your printer and printer driver (ie whether they support legal paper size - or have an option to specify custom page dimensions).

Assuming your printer driver provides an appropriate print setup option, you should select it first. If your layout is a list layout it will autpomatically adjust (ie include additional records to fill up the longer page length).

However if you are using a form layout, you may wish to go into layout mode and increase the size of the 'body' layout part (by dragging the part flag at the left) to fill the page length. A dotted line will appear to show you where the page ends, so you should position the part boundary just inside it.

With these simple adjustments you should be able to print appropriately formatted legal paper output.