PDFCreator allows you to easily merge multiple documents into one PDF file (or any other output format).
Follow the steps in Create a PDF to print a job into PDFCreator, but leave the print job in the PDFCreator window. You can now add more documents the same way.
You can use the Merge button to view the list of print jobs.
Hint
If you like, you can still add more print jobs while this window is opened.
In the list of print jobs, you can rearrange the order of the print jobs, delete individual jobs or wait for more documents. When everything is arranged, you can click on Merge all to combine the print jobs into a single document.
Now you can continue with the conversion and receive a PDF, that contains the pages of all source documents.
Hint
To add a PDF file to the merge window, you do not need to print it. You can either simply take it and drop it to the window or start a PDFCreator conversion via the context menu via right-click. Thereby you keep the original PDF without possible side effects by the printing.