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.
Invoice example With GST & PST An invoice not only shows the customer or client how much money is due but provides tax information, in some countries multiple taxes may apply, for example in Canada it is required to put the Supplier's identification numbers for GST and QST taxes purposes. Whenever a taxable sale is made, the customer must be informed that GST and QST are added to the selling price. As there are no standard invoices required by law for this purpose, you must indicate the amount of the taxes on the cash register receipt; on the invoice or contract remitted to the customer. If you choose to indicate the GST and the QST, the amounts must be stated clearly.The European Union requires a VAT (value added tax) identification number on invoices between entities registered for VAT.