So, I think the best ways to do this are as follows:

1. Go to the first Invoice then put a check mark  on the "Print Later" box at the upper middle portion of the screen of your invoice then click Save.

2. Proceed to the the second invoice, put a check mark also on the "Print Later" box then Save.

3.  Same steps follow on all the invoices needed to be merged.

4. After choosing and marking all the invoices, go to File, select Print Forms, click Invoices. A box will prompt up showing all the invoices that you selected to combine and print. This process will let you print and save these invoices into a single PDF file. Hope this helps. Your welcome :) - Rachel H.