How to change page orientation of PDF? (Ghostscript or PostScript solution needed)

Why do you require usage of Ghostscript? Would it be acceptable to use another Free, Open Source Software tool running on the commandline, such as pdftk?

Anyway, here is how to rotate pages with Ghostscript. However, this may not work for your intentions, because you cannot force a certain orientation for an individual page only. It relies on an internal Ghostscript algorithm that tries to rotate pages automatically, depending on the flow of text inside the PDFs:
* -dAutoRotatePages=/None -- retains orientation of each page;
* -dAutoRotatePages=/All -- rotates all pages (or none) depending on a kind of "majority decision";
* -dAutoRotatePages=/PageByPage -- auto-rotates pages individually.

Add one of these to the Ghostscript commandline you're using.

If there is no text on a page (or if there is an automatic page rotation set to /None), then Ghostscript uses the setpagedevice settings. You can pass such setpagedevice parameters on the Ghostscript commandline using the -c switch like this:
* -c "<</Orientation 3>> setpagedevice" -- sets landscape orientation;
* -c "<</Orientation 0>> setpagedevice" -- sets portrait orientation;
* -c "<</Orientation 2>> setpagedevice" -- sets upside down orientation;
* -c "<</Orientation 1>> setpagedevice" -- sets seascape orientation.

Probably you need to set the orientation for each page when extracting the pages. I don't think it would work when merging them back to the unified document (I have never tested this).

In any case, I'd recommend to look at pdftk too (which is also available for Windows). It is a commandline tool that can rotate pages from PDFs, and much more. Easier to use than Ghostscript for your stated purpose, and much faster as well. Especially, it can rotate individual pages inside a PDF document, leaving the other pages untouched. Example:

pdftk A=in.pdf           \
  cat A1-3 A4west A5-end \
  output out.pdf

This command will output pages 1, 2 and 3 as well as pages 5, 6, ... last un-rotated, but will rotate page 4 by 90 degrees (so the page header faces to the "west"). _{(However, be aware that this command can lead to unexpected results, depending on the original orientation of your input pages: You should check the orientation of all pages of your input PDF by running pdfinfo -l 1000 input.pdf and then check for the value of the rot output: if you see values different from 0, like 90, 180 and 270, these pages are already pre-rotated...)}

See here for more details: http://www.accesspdf.com/pdftk/ .

Nothing else than -dNORANGEPAGESIZE worked perfectly for me.