Dropbox is a popular free software that sync files between your desktop pc and laptop.When you installed Dropbox and set the Dropbox folder.All files/subdirectories from the folder are two-way synced to Dropbox server and can be downloaded/synced in another machine with Dropbox Client installed.
The point is only the files within the Dropbox folder can be synced.New edited file in another directory you want to sync must be copied to this folder.And you need to edit this copy in Dropbox folder to sync any change because changes in previous file don’t take effect.
Fortunately,in Ubuntu we can use symbolic link to make Dropbox sync files beyond the Dropbox folder.

All we need is this script: nautilus-dropbox-script.sh by W.H. Kalpa Pathum

How to Use this script:

1.Click previous link to download the script and edit it with your favourite editor.
2.Find DROPBOX_DIR=”$HOME/Dropbox/” and replace $HOME/Dropbox/ to your Dropbox folder (or its subdirectory).
3.Move the changed script to ~/.gnome2/nautilus-scripts/ directory.
4.give it execute privilege:

cd ~/.gnome2/nautilus-scripts
chmod +x nautilus-dropbox-script.sh

Now,create or edit a file anywhere beyond the Dropbox folder and in its right-click menu you can choose to sync to Dropbox.

Useful Link:
Download Dropbox (deb package)

How to install Dropbox in Ubuntu

Sign-up for a dropbox account