FoxIT's free PDF reader[0] has a Fill & Sign feature. And, it also allows you to type text anywhere on a PDF, in case that's what you actually want.
It's available for PC, Mac and Linux. (While the Linux version isn't as full-featured, I'd expect/hope all the versions have these 2 features...though I see that the feature-matrix on their website shows the Linux version doesn't have the Form Filling feature that the other versions have, FWIW, so it might lack one or both of the features I've mentioned).
The Fill-and-Sign feature is accessible from the Home tab -- there's a tool right end of the ribbon called "Fill & Sign".
The text-typing feature is also accessible from the Home tab: you choose the Typewriter tool from the ribbon, move the cursor where you want the text to show up, click there, then start typing -- the text will show up in a faint box (which disappears when you e.g. click somewhere else).
Later, you can click the Typewriter's arrow cursor on the text and the box will reappear -- you can then delete the box and its text, if you like, or you can double-click inside the box and get a text-cursor, which you can use to delete/add text.
I've used the Typewriter a bunch -- it works pretty well. (I think I've used Fill & Sign in the past, but not as often).
It's available for PC, Mac and Linux. (While the Linux version isn't as full-featured, I'd expect/hope all the versions have these 2 features...though I see that the feature-matrix on their website shows the Linux version doesn't have the Form Filling feature that the other versions have, FWIW, so it might lack one or both of the features I've mentioned).
The Fill-and-Sign feature is accessible from the Home tab -- there's a tool right end of the ribbon called "Fill & Sign".
The text-typing feature is also accessible from the Home tab: you choose the Typewriter tool from the ribbon, move the cursor where you want the text to show up, click there, then start typing -- the text will show up in a faint box (which disappears when you e.g. click somewhere else).
Later, you can click the Typewriter's arrow cursor on the text and the box will reappear -- you can then delete the box and its text, if you like, or you can double-click inside the box and get a text-cursor, which you can use to delete/add text.
I've used the Typewriter a bunch -- it works pretty well. (I think I've used Fill & Sign in the past, but not as often).
[0] https://www.foxit.com/pdf-reader/