flpsed (WYSIWYG PostScript annotator)

flpsed is a WYSIWYG PostScript annotator. You can't remove or modify
existing elements of a document, but flpsed lets you add arbitrary
text lines to existing PostScript 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, et cetera.
