How can I cover a window on an exterior door?

You could use contact paper.

How about a window film?

https://windowfilmworld.com/collections/privacy-window-film

https://www.decorativefilm.com/specialty-one-way-visibility

https://www.decorativefilm.com/

Also sold at hardware stores, big box home improvement centers. Depending upon where you live, selection might be better on line.

You can use window cling to create more privacy. https://www.hometalk.com/diy/windows-doors/windows/3d-window-cling-43405001

Etching the glass

Yes, they make film for windows that many people use on bathroom doors. They are put on with just dampness wiped on the back and stay as long as you like (mine have been on for years) so they are easily removed. BUT my point is that I used them on the front door windows. You can get them in many decorations with geometric or flowers (like mine) or many other designs. We got ours at Walmart, but you can order them online at Amazon also. They let in light, but are not see through. Here is a tutorial on how we did ours. I hope this helps! https://www.hometalk.com/diy/windows-doors/windows/ez-stain-glass-windows-39287626

Tammy....I believe you will find contact paper for that very use. I have some in a basement bathroom.

Hi ! Yes !!! At home depot or Lowe's they sell privacy film . It's like a contact paper for Windows . You cut it to size and stick it to your Windows . They have quite a few choices , some patterned some frosted ..with different amounts of visibility .

There are many desgns of privacy and stained glass window film. Amazon has the best selection. https://www.amazon.com/s?k=privacy+and+stained+glass+window+film&ref=nb_sb_noss_2

We hung a Roman shade over the window on the back door of our home.

Privacy film would probably be the best way.

Yes you could get a contact paper film that sticks on and you can’t see through it get it at Home Depot

The most professional way to cover a door and offer privacy would be to have a frosted or reflective window film installed on the door. The frosted film option will provide 24/7 privacy looking in and out and depending on which option you choose can allow a substantial amount of light to pass through.

The mirror film option would only provide privacy during the day but you'd be able to see out. At night however, people from outside will be able to see in.

https://privacyfilms.com/collections/privacy-films

Hi! I use window film for privacy. A friend did something a bit different. She mounted artwork over the window. You could hinge it, so that you could look out to see who is at the door. Good luck!