Have a copy of your resume and cover letter as a PDF.
A lot of recruiters are like the rest of the world, they use their phones to do work. They are so many different formats your resume and cover letter can be looked at. It should be something you think about when you’re formatting your cover letter. Saving it as a PDF can save the formatting work you’ve done to make the layout just right and guide their eyes to the important parts.
Try it for yourself. Save it as a PDF then check it on different devises.