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.
How to prepare an invoice _ examples and introduction _ Information that should be included in an invoice includes: A generic invoice should contain: The word "invoice" A unique reference number (in case of correspondence about the invoice) Date of the invoice Name and contact details of the seller Tax or company registration details of seller (if relevant) Name and contact details of the buyer/ customer _ Purchaser's name or firm name Date that the product was sent or delivered or the service or services rendered,or the work that was done. Purchase order number (or similar tracking numbers requested by the buyer to be mentioned on the invoice) Description of the product(s) _(sales invoice) or of the services ( service invoice) Unit price(s) of the product(s) (if relevant) Total amount charged (optionally with breakdown of taxes, if relevant) Payment terms (including method of payment, date of payment, and details about charges late payment) Discount,total before discount,and total after discount. (if relevant) Tax,total before tax,and total after tax. (if relevant) Shipping details if different from buyer details.The US Defense Logistics Agency requires an employer identification number on invoices.