I'll quote their feature list:
PDFCreator is a free tool to create PDF files from nearly any Windows application.
Key Features:
* Create PDFs from any program that is able to print
* Security: Encrypt PDFs and protect them from being opened, printed etc.
* Send generated files via eMail
* Create more than just PDFs: PNG, JPG, TIFF, BMP, PCX, PS, EPS
* AutoSave files to folders and filenames based on Tags like Username, Computername, Date, Time etc.
* Merge multiple files into one PDF
* Easy Install: Just say what you want and everything is installed
* Terminal Server: PDFCreator also runs on Terminal Servers without problems
* And the best: PDFCreator is free, even for commercial use! It is Open Source and released under the Terms of the GNU General Public License.
I never tried this though, cause I didnt need it so far
EDIT: I guess pdfcreator uses a queue for this... you will have to reprint your existing pdf with pdfcreator adding it to its queue then print your new file (whatever format, could be doc etc), adding it as well to the queue and then choose to combine your queue. Reads much more complex that it is actually . Basically hit print twice then say merge or whatever pdfcreator will call it
EDIT2: You can actually use inkscape for this as well I assume, if you have ghostscript installed you can simply import any pdf into inkscape. The Inkscape pdf import is pretty much amazing.
EDIT3: Link to ghostscript - choose the windows installer - the 3rd one (I assume you use windows JF )