Two-sided printing - variable length letters - from a single PDF

[CathyO-Xerox]

Hello biddybiddyheybuck,

I searched the Knowledgebase, and the only thing I can find on Variable data printing is how to add slip sheets to output, and I don't think that is what you are looking for. So I would recommend contacting the Support department and ask to speak to a product specialist for more help: 1-800-821-2797

[biddybiddyheybuck]

I support a hospital who sends letters to patients to inform them of upcoming appointments. These letters can be one, two, or three pages long, depending on number of appointments, special instructions, etc..

Currently, these letters are printed to a PDF file overnight, which is fed into the Colorpress 1000i the next morning. The machine apparently prints the letters (double-sided) and stuffs them into windowed envelopes. 

The problem, as you can imagine, is that the variable length of the letters is not handled well when printed two-sided. Examples...

If the first letter is two pages, then the first page is on the front side of the paper and the second page is on the back side of the paper. Perfect so far.

If the second letter is three pages, then the first piece of paper contains page one (front) and page two (back) and goes in the first envelope. The second envelope contains the third page of the previous patient plus the first page of the next patient. Yuck.

How is this functionality intended to be used? Should each letter be its own PDF? If only one PDF, is there a way to communicate to the printer that "this letter is done, stop printing, put these papers in an envelope, and move on to the next letter"?

Any advice or recommendations are appreciated.