"Get Info" (via ⌘-i) generally holds a wealth of information and can be used to "tailor" a bunch of stuff.

Recently I recalled an ancient .rtf Word document which did not in its file designation contain the extension. (Aside: Most icons indicate the nature of the document — eg, RTF, PDF.)
I sent it via an email attachment, retaining a copy of same for myself, but when I examined it and then downloaded it, the attachment came up as an .mds document — something I had never seen or even heard of before. It looked like the original .rtf document, but there were some subtle differences. (Suffice it to say that I attached the .rtf extension, re-sent it, and all was right with the world.)

Another aside: I designate all Word files as .rtf (rather than .doc or .docx) because at least in the past many recipients could not open Word documents; .rtf at least allowed such. Moreover, with very little difference in appearance, .rtf specification allowed the size of the document to be very much smaller (at least 80% smaller) than the equivalent .doc or .docx document.