PlansXpress is not an image editor, it cannot be used to rotate a PDF, JPG or BMP file however a PDF (or JPG or BMP) can be rotated before being imported to PlansXpress using a free image editor called Gimp.
You can download Gimp from www.gimp.org
When you open Gimp, you should see a window similar to the screenshot above.
Click File > Open...
Locate your PDF, click on it and then click Open.
You will see a preview of the PDF, click Import.
You will now see your PDF displayed in the Gimp workspace.
On the top menu click Image > Transform. From this menu you can click to Rotate 90° clockwise or Rotate 90° counter-clockwise.
Once you have rotated the PDF, click File > Overwrite <your PDF file name>.pdf
The PDF will now be saved in the correct orientation and is ready to be imported into PlansXpress.