-Install ["krop"]http://arminstraub.com/software/krop

>$ sudo gdebi krop_0.4.8-1_all.deb

Run the program:

>$ krop

Gui will guide you how to crop your files. Rotation option is also available!

-For combining your seperate 'pdf' files you can use 'pdfunite'. On the terminal:

>$ pdfunite inp1.pdf inp2.pdf out.pdf