I downloaded a PDF where the page was scanned in Portrait mode but the info was in landscape which meant I had to flip it on it's side to read it properly.
I use SumatraPDF from www.sumatrapdfreader.org/free-pdf-reader.html
Using this program I can easily flip it by going into settings, the three stacked lines in the top left hand corner of the program.
Then I click on View and Rotate Right. One problem I can not save it in that rotated format, which is what I want to do. Checking on-line I found a ton of on-line services offering to this for free but I wanted a program on my system.
I found one at www.pdfill.com/pdf_tools_free.html
It's called PDFill_FREE_PDF_Editor_Basic.
Download install and open. At the time of this writing no add-on junk to worry about. They offer a few tools here that may come in handy but for now I'm only interested in one.
No. 4. Rotate or Crop PDF Pages.
Click on it. Choose your file.
In the next window check the All Pages box. Then Rotate by and in the box that says 0 Degrees click on it and click on Clockwise 90 Deg (or whichever way you want to rotate it) and then Save As... Put and a name for your rotated PDF and choose your folder where you want to save it.