First find your database file by opening Invoice Expert and looking at the very bottom of the screen:

Usually it's located in: C:\ProgramData\Invoice Expert\PCInvXE.vdb4

Sign up for Dropbox and log in to your account. Then upload your database file.

Follow those screenshots below to get the link to a file in Dropbox:

Navigate to the database file you found above:

You should now see:

You can email this link by right clicking and then selecting paste. The link should look something like:

https://www.dropbox.com/s/eog5cttmo9n2ozg/PCInvXE.vdb4