If you are permitted to submit your invoice via email then it is useful to convert the invoice into PDF format so that it cannot be altered. There is a free PDF creator which you can use at PDFCreator. This creates a PDF file from any application which can then be emailed to the client. Better off, if you can use a software system, it will automatically generate invoice in PFD format, you can also email it straight away from within the a software program.
As mentioned for the quotation, the points to be included in the proforma are: 1.Seller's name and address 2.Buyer's name and address 3.Buyer's reference 4.Items quoted 5.Prices of items: per unit and extended totals 6.Weights and dimensions of quoted products 7.Discounts, if applicable 8.Terms of sale (include delivery point) 9.Terms of payment 10.Estimated shipping date 11.Validity date