Are letterhead and signatures necessary in the LOR?
In this era of networked printers, few people ever actually load letterhead paper into a printer any more.  Instead, most organizations have electronic &quot;identity&quot; or &quot;branding&quot; collections that include templates for letterhead, business cards, etc.
As such, in my experience, most recipients (in the US and Europe at least) expect letters to arrive in PDF format. Many will not even allow a letter to be sent physically any more.
For most recommenders, then, using &quot;letterhead&quot; just means taking care to use the fancy formatting to make a good impression, just like one might wear formal clothing to make a good impression at a fancy event.  In dealing with academics, however, eccentricity is to be expected, and variation from norms is often tolerated.
Bottom line: your recommender should probably be able to use letterhead electronically. If for some strange reason they can't, it shouldn't be a big deal, as long as it's still easy to tell they are a real and respectable person (e.g., emailing from an institutional address).