In the event that your PDF is rotated incorrectly when using the Share File option in Webex, you can use this guide to correct the issue. The guide will take a few minutes, so it may be more time-appropriate to share your whole screen and then fix the PDF later.

https://help.webex.com/en-us/WBX17725/Landscape-PDF-Document-is-Shared-in-Portrait-View-Using-Presentation-or-Document-Sharing