Saving documents

1 how do I save a letterhead in a way that client can use it both for print and digitally. (i don’t think they can use the pdf)
2 Can i save something on illustrator as a jpeg?

For the letterhead you can put it into a word document as a locked image in the background or as a watermark and then send them the word doc so they can use it digitally. for print the PDF is just fine!
Save in illustrator as a JPG go to file, export and then choose JPG from the dropdown menu

thank you so so much