I have been sending invoices to my customers via email and there has been no problem till recently but only 1 customer has complained. The last 2 weeks the invoices are not opening. could this be a problem in relation to windows 10? or the customers PDF viewer?
Easy enough to test no, if you can ask the customer to email the PDF back to you? If you can open it, has to be a problem at their end. This seems likely anyway, given that they’re the only customer to say anything.