Delimited Text File (CSV,TXT) - see Text Import Settings.
It's also very helpful to have example files that can be used to test with.
An actual specification document is great but often vendors have internally developed Matlab importers that can be used outright or be modified to work.
We're always happy to develop (or help develop) file importers.
Obtain a file format (specification) from the vendor.
Other sources exist as well, for example: CDF Tools.
Locate a community developed importer on the Matlab file exchange.
Create a custom import function Editds_userimport.
For more information on using the textreadr function see Textreadr.
If data can be exported as text, some customization can be done via our text importing tools to accommodate different formatting:.