Its a good idea to have a no BS method of merging pdfs and/or images together into one pdf from the terminal. Here are couple ways to do so.

# imagemagick - merge multiple pdf's or images into one pdf
convert file1.pdf file2.jpg file3.png merged.pdf

# ghostscript - merge multiple pdf's (this may have nicer results)
gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOutputFile=merged.pdf pdf1.pdf pdf2.pdf

Related External Links:

• Super User - how-to-merge-pdfs-using-imagemagick-resolution-problem