What you describe seems to be about the orders you create in WooCommerce, not the invoice that our plugin creates for it (which is just a PDF file).
WooCommerce has 2 settings that could affect whether an order is still payable or even on your site at all:
- WooCommerce > Settings > Products > Inventory: if you have enabled Manage stock, you’ll be able to set a number of minutes here that stock is held with the option Hold stock (minutes) (one week would be 10080 minutes which I believe is the default). After this time, the order will be canceled and can no longer be paid
- WooCommerce > Settings > Accounts & Privacy: there’s a setting Retain Pending Orders where you can set the time that a pending order will be kept on your site. After expiration it will be deleted. I believe this option is not enabled by default.
Hope that helps! If you have any further questions about this particular issue I suggest that you post them to the WooCommerce forum instead. Of course, feel free to open a new thread if you do have other questions related to PDF invoices & packing slips!