Yes, updates are lifetime but for versions which start with 3.x number. Currently there is no higher version but it can change in the future.

Yes, program offers backup and restore feature. You can read more in help section: Backup and Restore

Program is installed in Program Files on disc C. But your data is stored in the Application Data folders at C:\Users\username\AppData\SimpleInvoice. AppData is hidden folder in Windows System.

Currently work in network is not available and I don not plan to add this feature in the close future.

No, currently multiple currency is not available. I would like to add this feature in the future.

No, currently Purchase Order is not available. I would like to add this feature in the future.

No, payment receipt is not available. Available is sales receipt.

Yes, program offers Import and Export feature. Currently you can import/export Products and Customers. You can read more in help section: Import and Export

No, Simple Invoice works only under Windows system. I do not plan developing Simple Invoice to other platforms.

Yes, but languages in the Simple Invoice software were made thanks to other users. If you want you can make translation and I will add it to program. You can contact with me.

You can use Backup and Restore option. Read more in help section: Backup and Restore

Yes you can use barcode reader with the software. Please read Barcode reader topic.