Good news, you don’t need to deal with either of them to submit a file to PrintPlace.
Both the Reader’s and Printer’s Spreads are tools used to visualize how a digital document will be printed on a press or bound into a book; the practice is known as imposition. The Printer’s Spread shows the layout of pages, like they would appear on a press so the front and back of each page are lined up and the some of the pages are inverted as necessary so that the final print order will work out right. The Reader’s Spread just shows the pages as they will appear once everything is bound up into a book format, so pages 2 and 3 will show together, for example (since the left page is always even numbered).
Some printers may like to see your files in one of the spread layouts. Not us. We want a multi-page PDF file in sort order. That means that page 1 is first (and by itself), page 2 is second, and so on. Note that the first page of the PDF should be the cover of the booklet, page 2 is the inside cover and page 3 is the first interior page. Continue the pages until the outside-back cover. Nothing needs to be combined, re-sorted or flipped. We’ll take care of all of that for you (and we’re happy to do it). Just keep all the pages in the same order you want them to appear in the final document.
Remember, though, that if you order a 16 page booklet, you need to give us a 16 page file. If you plan on the last page being blank (or another page within the booklet) that’s fine, you just need to include that blank page in the artwork you upload to us so we know where to put it. If we get a file with more or less pages than you ordered we won’t be able to process it and the file will not be accepted for rendering by our proof-generating software.
If you need help with your files, send us an email to firstname.lastname@example.org or call us at 877-405-3949. We’ll be happy to help.