Does a PDF invoice also have to meet accessibility requirements?

PDF invoices are usually also subject to the requirements

Yes, a PDF invoice that is provided to a customer through a webshop or service is in most cases subject to the same accessibility requirements as the rest of the site. It is not about which file format a document is in, but whether it is part of a service that falls within the scope of the law. An invoice that a customer automatically receives or can download after placing an order is part of that service provision, and therefore the requirement applies: someone using a screen reader must also be able to read and understand the invoice.

In practice, this means that a PDF cannot be a scanned image of text, that the reading order is correct, that tables (for example with amounts and VAT) are recognizable as tables for assistive software, and that information is not conveyed only through colour or shape. These are the same kinds of requirements that apply to the rest of a webshop, and which are brought together in what WCAG 2.1 level AA means in plain language. For businesses uncertain whether their company is subject to the law at all, that is a separate question that stands apart from the PDF format itself — see whether the accessibility law applies to a webshop.

Why this follows from the standard

EN 301 549 and the underlying WCAG 2.1 guidelines make no distinction based on file format: the requirements apply to content that is part of a service, and this includes documents such as PDFs provided as part of that service, in addition to web pages. An automated scan can check some of the technical structure in a PDF invoice — for example, whether tags are present and whether the text is recognizable as text — but cannot assess whether the reading order makes sense for a screen reader or whether a table is logically structured. This is one of the points that comes up in every report as something that cannot be determined automatically.