Last week I talked about taking a paper document and scanning the document. CRA is ok with this as long as the document is legible. CRA does not give you options if the document was created electronically.
A document that was originally produced as an electronic form must be kept in electronic readable format, even if you have a printed copy. For example, if you generate your sales invoices with an accounting program, then you have to keep those invoices in an electronic form. This generally means that you will keep the accounting software for as long as you are required to keep the documents.
Another option is to export your accounting records to Excel or other spreadsheet program so that the documents can be accessed electronically. This, of course, is an additional requirement, having to maintain the electronic version.