app-text/mupdf is a free and open-source software framework written in C that implements a PDF, XPS, and EPUB parsing and rendering engine. In Gentoo, several packages like app-text/llpp or app-text/zathura-pdf-mupdf use it internally for pdf rendering.
Binaries installed by MuPDF are:
MuPDF is said to provide optional support for interactive features such as form filling. However, documentation of these features seems well hidden.