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: