If are using Metastock from a 3rd party provider you will need a BullCharts Metastock key to read the data from a 3rd party. Once you have the key, then a new menu in File will display Open Metastock.
If you are a subscriber to BullCharts data, there is an option to export BullCharts data to Metastock to use in other programmes. You do not need a BullCharts Metastock key to export data to Metastock.
Open a chart using Metastock data
File/Open Metastock