Although I am still not quite clear on what this system is ultimately needed to do, ...
Is your main question here "architectural" ("How do I design this"), ...or technical (How do I create a text file specification)?
If what you posted is a sample of some actual source Data, then this will have to be "Parsed" to something like this:
tblSales:
InvoiceID (Primary Key)
SaleDate
CompanyName
CompanyAddress
CompanyCity
CompanyState
CompanyZip
VendorNum
InvoiceNum
tblLineItems
LineItemID(Primary Key)
InvoiceID (Foreign Key)
ItemName
ItemPrice
Now, this is just a basic framework.
Depending on what you ultimately need and your business rules, you may need to create Customer Tables, product Tables, ...etc
So again, if what you posted is a sample of the source data, then a great deal of work needs to go into converting it into a standard database (table) format
JeffCoachman