SQLite .sqlite file gets corrupted when exported

I'm currently creating a simple database for a college project via SQLite Database Manager FireFox plug-in. However, I exported the database and I have these two files; Mia's Sandwich Shop.sqlite and Mia's Sandwich Shop.sql my next step was to implement FOREIGN KEY constrains via notepad++ which I did and saved it. Next thing I've done is tried to connect to the database file Mia's Sandwich Shop.sql via the SQLite plug-in in order to update the .sqlite file. However, I'm constantly stopped by this error:

SQLiteManager: Error in opening file Mia's Sandwich Shop.sql - either the file is encrypted or corrupt Exception Name: NS_ERROR_FILE_CORRUPTED Exception Message: Component returned failure code: 0x8052000b (NS_ERROR_FILE_CORRUPTED) [mozIStorageService.openUnsharedDatabase]

Initially I thought that I've somehow corrupted the database, but then i tried opening only .sqlite file and exporting it to .sql (i.e. original and unchanged) and the try connecting to it without performing any changes, but I still get the same error.

Any help will be greatly appreciated.