Stationery is a mass noun referring to commercially manufactured writing materials, including cut paper, envelopes, writing implements, continuous form paper, and other office supplies. Stationery includes materials to be written on by hand (e.g., letter paper) or by equipment such as computer printers.
A large amount of the content of this article confuses the general term stationery—which covers everything from cheap paper for using in inkjet printers, to velum or other unusual papers with personalised letterheads, and from the cheapest bic pen to fountain pens costing many thousands of dollars—with the more specific meaning of fancy or customised paper products usually used for invitations, thank you cards, etc. The article should be rewritten to mark this distinction. It might even make sense to separate out the second topic into its own article on “customised stationery” or something similar.