Citrix / Webex work by sending from the server to the client machine only the actual changes in the screen that is being viewed, and not the whole screen. The rationale of their approach is that much of the commercial nature of transfers is character based, often with a (relatively) small number of characters being changed in any one screen format.
In order to make it more difficult for the wide variety of screen capture methods and techniques to function, or to function effectively, we do not send information in a character based form to the screen, but render it to the screen as a full-screen graphic.
Further, if the option to use enhanced screen grabbing is engaged, what this does is to tell our viewer to render more than one image to the active screen, only one image of which has sufficient opacity as to be seen by the human recipient. Of course, the effect of this is to launch an enormous amount of screen rendering from the Viewer application to the screen. For the normal PC screen there is a noticeable performance effect because of the multiple rendering, but it is not catastrophic. However, if engaged in a Citrix / Webex environment it may cause much higher bandwidth demand than is normal.
The same applies to printing in these environments because we do not send print that is character based (it is graphic based), and overlay heavily in order to provide the number of watermark options that we support. This is to reduce the ability of the attacker to take their own copy and easily transfer it back to native PDF. All these things will increase transmission time and the amount of memory that will be required in order to transfer the print request to the output device.
Using the page up/page down keys instead of mouse scrolling will result in a performance improvement because there will be significantly less screen rendering needed to achieve the effect. Disabling enhanced screen grabber should also produce better performance results assuming that you are content with the downgrade of the security.