You cannot convert a SQL Server 2012 database file to a SQL Server 2008 database file. The downgrade is not possible. The compatibility of database files is available only from an old version to a newer one, not the opposite. Indeed, you can convert a SQL Server 2008 database file to SQL Server 2012 database file.
Use the integrated SQL Server tools:
- Right click on the database.
- Select
Tasks and Generate Scripts.
Following the wizard, at the end of it in the Advanced Scripting Options clicking the "Advanced" button, select the SQL Server version for which you want to generate the scripts, using the option Script for Server Version. Moreover, you would be able to generate the scripts to export the schema of your objects and/or the data, selecting the option Types of data to script, as you can see in the screenshot below:
The time needed for the process to generate both (schema and data) will depend on the amount of data you want to export, of course. As @Arun suggested, have a look at the process in more detail here, using step by step instructions.
