Basically there are 3 types of files used mostly. Apart from that there are many more formats but theses used more frequently.
QVW: Stands for Qlikview Worksheet (The application file which holds your reports/dashboard/script/data model and connection strings)
QVD : Stands for QlikView Data (One of the optimize layer of data which has been fetched from the database, qvd is a patent technology of QlikTech and QlikView applications reads data 100 time faster as compared to any other sources because data get stores in optimized format. Only Qlikvew application can read the data from QVD. Its always better to fetch the data from from database first and then load the data into your application)
QVX: Stands for Qlikview Data Exchange (If you wish to make your own connector that could create a connectivity to QlikView files, One of the efficient and optimize way to fetch data from the database. Mainly used if you are not using ODBC/OLEDB)