reply to u/MartyFunkhoosier at https://reddit.com/r/typewriters/comments/1r03411/1940s_underwood_correspondent_types_very_light/
How good is your typing technique? https://boffosocko.com/2025/06/06/typewriter-use-and-maintenance-for-beginning-to-intermediate-typists/
Typically you want to strike the key as if it were a hot coal and let the initial hit's momentum force the slug against the ribbon/paper/platen. If you're "bottoming your keys out" which happens more frequently when you hunt and peck, then you'll end up with a ghosting effect. Using your paper bale properly is important for clear imprints.
If your ribbon isn't well inked (it should color your fingers when you touch it or look "wet" if it's new) that can sometimes be an issue. Beyond that, platens tend to shrink and become hard with age. As a result the machine goes out of its original proper alignment thus making your imprints lighter. You can use a second "backing" page to help make up some of the difference, but a re-covered platen (J.J. Short Associates can help in the U.S.) and a proper ring and cylinder adjustment will likely help. And if you can't afford the recovered platen (~$120) then a ring and cylinder adjustment will help nonetheless. (Check Youtube for how you might do this yourself if a shop isn't nearby.)