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.
There are certain pieces of information that have to be on your invoices if you are charging GST, HST and/or PST. Your invoice must include: your business name. the date of the invoice. your Business Number (also known as the GST Registration Number). the purchaser's name. a brief description of the goods or services performed. the total amount paid or payable. the terms of payment. an indication of items subject to GST at 5% or HST at the appropriate provincial rate, or that the items are exempt, and either the total amount of GST/HST charged, or a statement that the GST/HST is included and the total rate of tax. if applicable, an indication of items subject to PST (also known as RST) at the provincial rate, or that the items are exempt, and either the total amount of PST charged, or a statement that the PST is included and the total rate of tax.