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.