If you receive a scanned PDF that should be landscape instead of portrait orientation, follow these steps to rotate and save the PDF document. For this method you'll need to be running Google Chrome, and you'll also need a PDF Printer installed such as Microsoft Print to PDF.
Open File Explorer and right-click the PDF doc you want to rotate. Then choose Open With > Google Chrome
Choose a PDF Printer such as Microsoft Print to PDF as the destination. Then click Print using system dialog... (Ctrl+Shift+P)
Open Preferences and change the Orientation using the drop down menu.
Click OK, Apply and Continue to create/print your new rotated PDF file.
Note: repeat the previous steps if the PDF document needs to be rotated a further 90 or 180 degrees.