> this is really a simple question that you are complicating beyond belief.
> why is that so complicated?
Well, if you want to drive a car, if you don't know about gears, clutches, and brakes, if you ask for informed advice, and if you are informedly advised of gears, clutches, and brakes, perhaps it's not the best approach to publish that you consider information about how to guide your vehicle on the road to be ... well, idiotically complicated -:). You would perhaps be better advised to listen, get hold of a book or two, and learn.
> if I create a page in PAGES and output that page as a PDF, can that PDF be 300 DPI?
> I am not putting an image in. I am creating a document and exporting as a PDF
> then opening in Preview and saving as a JPEG
> this is a simple process to get a hi res JPEG image to the printer
Sigh, Adobe PDF has no resolution per se. By definition, PDF, and PostScript from which it derives, is a co-ordinate space defined in two duodecissimal systems, US inches and US pica-points. Vector objects you define in the co-ordinate space also don't have a resolution per se, as Walt told you above.
In the page design phase, resolution comes into the picture for imported photographs. Here, if you don't place the right resolution in your originating application, in this case Pages, you don't magically get the right resolution in PDF (or PostScript, or PCL, or XPS ...).
Resolution also comes into the page design phase for a special class of vector-like objects in PDF 1.4 and higher, namely transparencies which may involve resolution-independent vector objects, resolution-dependent raster objects, or any combination of the two.
When you place a photograph for an album cover, write a title for the album on top of the photography, and apply a transparency to dim the busy photograph sufficiently that you reader is able to catch your title without studying it closely, then you have a combination of vector and raster objects in the transparency.
The PDF/X filter in the ColorSync Utility exists for two main reasons, (1) it lets you choose the ICC colour space conversion profile for the printing condition, and, (2) it lets you choose the resolution at which transparencies will be rendered when the PDF is created, not when it is consumed in the RIP.
I should probably write to advise you not to convert from PDF into JPEG, because JPEG looses detail by definition. I should probably write to advise you to choose the default TIFF format because it does not loose detail. But you would say that I am making things idiotically complicated.
Perhaps, by way of closing, you would tell us why you want to export from PDF to JPEG, and to JPEG at 150DPI to boot? I may have missed something, but I believe you and your printer wanted 300DPI?
Believe me, I appreciate that you find computing to be complicated. It is, as all agree. But it you approach the challenge in the belief that knowledge is needless, then you will find help only among the angels -:).
Best,
Henrik