mthelp errors: xpdf not found

[manojbaishya]

When I look for documentation in the command line with mthelp, I get the following error:

$ mthelp --view amsmath
/bin/sh: 1: xpdf: not found

Also, if I type mthelp amsmath, it opens a html list of documentation in Firefox instead of the default system browser (Chrome).

Expected behaviour: mthelp --view <package-name> should open in default PDF viewer and mthelp <package-name> should open in default browser.

How can I fix these?

System Info:

$ lsb_release -a
LSB Version:	core-11.1.0ubuntu2-noarch:security-11.1.0ubuntu2-noarch
Distributor ID:	Linuxmint
Description:	Linux Mint 20.1
Release:	20.1
Codename:	ulyssa

$ latex --version
MiKTeX-pdfTeX 4.6 (MiKTeX 21.3)
© 1982 D. E. Knuth, © 1996-2021 Hàn Thế Thành
TeX is a trademark of the American Mathematical Society.
using bzip2 version 1.0.8, 13-Jul-2019
compiled with curl version 7.68.0; using libcurl/7.68.0 OpenSSL/1.1.1f zlib/1.2.11 brotli/1.0.7 libidn2/2.3.0 libpsl/0.21.0 (+libidn2/2.2.0) libssh/0.9.3/openssl/zlib nghttp2/1.40.0 librtmp/2.3
compiled with expat version 2.2.9; using expat_2.2.9
compiled with jpeg version 80.0
compiled with liblzma version 50020042; using 50020042
compiled with libpng version 1.6.37; using 1.6.37
compiled with MiKTeX Application Framework version 4.1; using 4.1
compiled with MiKTeX Core version 4.5; using 4.5
compiled with MiKTeX Archive Extractor version 4.0; using 4.0
compiled with MiKTeX Package Manager version 4.2.1; using 4.2.1
compiled with openssl version OpenSSL 1.1.1f  31 Mar 2020; using OpenSSL 1.1.1f  31 Mar 2020
compiled with uriparser version 0.9.3
compiled with xpdf version 4.02
compiled with zlib version 1.2.11; using 1.2.11

[manojbaishya]

Quoting from mthelp docs, adding the following to ~/.profile solves both the problems above:

export MIKTEX_VIEW_pdf="okular %f"
export MIKTEX_VIEW_dvi="okular %f"
export MIKTEX_VIEW_ps="evince %f"
export MIKTEX_VIEW_html="google-chrome %f"
export MIKTEX_VIEW_txt="mousepad %f"