Intuit Interchange Format (IIF) files are delimited text files used for import and export operations with Intuit data files, such as a QuickBooks company file (.qbw).
In QuickBooks, IIF files have some important limitations, which are discussed in this Intuit knowledgebase article. These files:
- can’t be used to import linked transactions, such as a link between a customer invoice and a customer payment paying for that invoice
- can only be used in single-user mode and logged in as the Admin user
- can’t be used to import or export payroll data
- can’t be used to export transactions
Because of these limitations and the fact that Intuit doesn’t support their use, IIF files are increasingly becoming obsolete.