Combine multiple PDF files into single PDF file

The following command will combine all the PDF files in current folder into a single file called all.pdf.

gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOutputFile=all.pdf *.pdf

Launch Custom Script at Startup

Say the name of the script is checkconnection.
Create the file :
.config/autostart/checkconnection.desktop

Add following lines to the file:

[Desktop Entry]
Type=Application
Terminal=false
Exec=/path/to/scrip/folder/checkconnection
Name=checkconnection

Permanently Save Brightness Settings

Issue the command: 
crontab -e

This will open vi editor. Type the following line, save and exit vi editor (:wq).

@reboot echo "5" > /sys/class/backlight/acpi_video0/brightness