PDF stands for "Portable Document Format". The PDF file format is used to create documents that will display identically on all systems and under all screen resolutions.
Any document created in Atlantis can be saved as a PDF file, i.e. automatically converted to the PDF format, provided that a "virtual PDF printer" is installed on your PC. Please note that these virtual PDF "printers" do not actually print documents, they only place a PDF version of the original document on your disk.
If your system has no virtual PDF printer, you will find related links in the "Free Tools" section of the Atlantis Downloads page. When you have installed one or several of these virtual PDF printers on your system, they can be selected from the "Printer" box of the Atlantis "File | Print..." dialog. Here is a sample screen capture with two virtual PDF printers listed among the printing devices in the Atlantis "File | Print..." dialog:
Here are the steps to save the active document as a PDF file in Atlantis: