If you have a bunch of pdfs (e.g. like tables, figures, or manuscript as separate pdfs) and want to combine them into a single pdf for uploading to a journal:
First make sure you have ghostscript (check Program Files for "gs"). If you don't have it, download from http://www.ghostscript.com/download/gsdnld.html and run the .exe file.
In Notepad (or other text editor), put the following command:
@echo off
"C:\Program Files\gs\gs9.06\bin\gswin64c.exe" -sDEVICE=pdfwrite -dNOPAUSE -dBATCH -dSAFER -sOutputFile="alltables.pdf" table_1.pdf table_2.pdf table_3.pdf table_4.pdf table_5.pdf table_6.pdf table_7.pdfwhere "alltables.pdf" will be the output file, and table_1.pdf...is the list of your pdf files.
Save the text file as a .bat file in the directory that has the pdf files. To do this in Notepad, save the file using " " marks: "pdfcombine.bat"
Now, double click on the .bat file in Windows Explorer, and you should see your "alltables.pdf" file.