Unless I'm misunderstanding, to get your family tree printed "in the pdf format" you would do the following:
1. Select the "anchor" person for the tree, then select the number of generations for parents, and then for children. If you want to include additional generations of the children of the anchor's siblings, also select the number of generations of "Others". These are all at the bottom of the webpage.
Note that what you see on the screen is (approximately) what your PDF document (or printout) will look like.
2. Click on the Print link at the beginning of the first line at the bottom of the screen. The sidebar (on the left of the screen) will change to the "Create a PDF for printing" dialog. Here, select your paper size, orientation, # of pages for width and # of pages for height. If your tree doesn't fit on your screen, you should increase the width and/or height to accomodate for how large the part of your tree you wish to print/export to PDF.
3. Click the Download PDF button in the dialog box on the left, then a new dialog popup box will open asking if you want to save your PDF or open it. I usually choose to open it so I can review how it looks and make adjustments if necessary (e.g. adding or removing pages of width or height).
4. If you choose to Open the PDF for review and are happy with the results, you can simply print it from the PDF reader, or close it and go through steps 2 & 3, this time selecting to Save the PDF.