thanks for the video, it seems something unexpected is happening on your end, I wasn’t able to reproduce the issue here.
Usually, after clicking on merge you should more or less instantly get the following merge window:
In general, you can first print all the documents you’d like to merge to PDFCreator (without pressing any button on the PDFCreator GUI) and at the end use the merge button.
Please set the logging level to “trace” inside the PDFCreator application settings, reproduce the issue and send the resulting log to support(at)pdfforge.org
, it should help to find the cause of the issue more quickly.