flpsed binary package in Ubuntu Focal amd64

 flpsed is a WYSIWYG pseudo PostScript editor. "Pseudo", because you can't
 remove or modify existing elements of a document. But flpsed lets you add
 arbitrary text lines to existing PostScript 1 documents. Added lines can
 later be reedited with flpsed.
 .
 Using pdftops, which is part of xpdf, one can convert PDF documents to
 PostScript and also add text to them. flpsed is useful for filling in forms,
 adding notes, etc.

Source package