How to generate the PDF file:

Assuming your extended abstract and extended version are in the same folder, and respectively named "submission-abstract.pdf" and "submission-full.pdf", here is how to generate a merged file "submission.pdf" from them:

* Under GNU/Linux (assuming the PDF Toolkit [1] is installed):

cd <folder of the submission>
pdftk submission-abstract.pdf submission-full.pdf cat output submission.pdf

* Under GNU/Linux (using only Ghostscript, usually installed by default):
cd <folder of the submission>
gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -dPDFSETTINGS=/prepress -sOutputFile=submission.pdf submission-abstract.pdf submission-full.pdf

* Under Microsoft Windows (Windows XP, Vista, Windows 7 and Windows 8):

This can be done using additional software; we list below two possible options, but more can be found (with examples of how to use them) on [2]:
 - PDFTk (Free; can be obtained from [1]); or
 - Adobe Acrobat

For the latter (Adobe Acrobat):
	- click on "Create" button, in the main toolbar.
	- in the dropdown menu, select "Combine Files into a Single PDF"
	- on the new window that appears, choose "Add Files" and choose and add the two files "submission-abstract.pdf" and "submission-full.pdf"
	- once they appear in the previous window, order them in the right order ("submission-abstract.pdf" on top) using the arrows at the bottom
	- uncheck "Include all open PDF files", then press  "Combine Files" in the bottom right corner.
This should generate the merged PDF; it only remains to save it via "Files > Save As...".

* Under Mac OS X (10.6 or later)
"Preview" is able to combine PDF files; detailed instructions are available on the Apple website: http://support.apple.com/kb/ht4075


[1] https://www.pdflabs.com/tools/pdftk-the-pdf-toolkit/
[2] http://www.wikihow.com/Merge-PDF-Files