That FAQ's reference to changing preview format settings appears to be out of date, and has been reported. The setting was removed some time ago, and caching was improved. What version of Videopad is being used? Here is the latest.. https://www.nchsoftware.com/videopad/vppsetup.exe For licensed users upgrades are free for up to six months. After that, VP will continue to fully function but a fee will be required in order to register the newest.
Let the green cache line (above the timeline) complete before previewing. If the buffering issue still exists use proxies for the 4K files. This is a common practice with many NLE systems, to make large files more manageable for editing.
Quality does not suffer, original files are used for the export. http://nch.invisionzone.com/topic/26563-proxy-editing/
Please share your project, or a portion thereof that displays the issue, so the developers can analyze what may be causing sluggishness. Folks will work with you and if a problem is found you may get a free license.
Sharing is not difficult. Here's how... http://nch.invisionzone.com/topic/23659-tips-for-getting-help-on-this-forum/
If it contains sensitive material you can link it in a personal message (PM) to me, via the envelope above. Be sure to FILE|SAVE PORTABLE PROJECT AS, not simply SAVE PROJECT, and don't forget to share it.