Is there a way to rotate pdf pages in the Texstudio pdf viewer? I don't find any command for that.
There's a feature request (submitted in 22-dec-2012) in the TeXstudio web site, asking for that specific functionality (the ability to rotate the page in the PDF viewer). So, I'm guessing it's not possible to rotate pages, when using the integrated PDF viewer. Here's the link to that Feature Request:
TeXstudio - A LaTeX Editor / Feature Requests / #373 Rotate page in pdf viewer http://sourceforge.net/p/texstudio/feature-requests/373/
EDIT: As a workaround, if you have a PDF viewer installed in your system that supports rotation (like Evince), then you can set up TeXstudio to use an "External PDF Viewer". You can do this in the "Options" menu -> "Configure TeXstudio..." command, choose the "Build" option, and change the selected option in the "Default Viewer" and "PDF Viewer" option to "External PDF Viewer". Here's a screenshot to help visualize what I'm talking about (I've marked the relevant options with a red squared rectangle):
You can use the authentic Texmaker which supports page rotation :