I have already described how to list the contents of specified package using apt-file utility, but you do not need it to check the contents of downloaded package.
I will use rsyslog-pgsq package to show you how to perform different operations.
$ apt-get download rsyslog-pgsql
Get:1 http://deb.debian.org/debian stretch/main amd64 rsyslog-pgsql amd64 8.24.0-1 [188 kB] Fetched 188 kB in 0s (7422 kB/s)
Display information about this particular package.
$ dpkg --info rsyslog-pgsql_8.24.0-1_amd64.deb
new debian package, version 2.0. size 187916 bytes: control archive=1724 bytes. 379 bytes, 18 lines * config #!/bin/sh 498 bytes, 15 lines control 563 bytes, 7 lines md5sums 1118 bytes, 43 lines * postinst #!/bin/sh 1459 bytes, 59 lines * postrm #!/bin/sh 124 bytes, 10 lines * prerm #!/bin/sh Package: rsyslog-pgsql Source: rsyslog Version: 8.24.0-1 Architecture: amd64 Maintainer: Michael Biebl <biebl@debian.org> Installed-Size: 219 Depends: libc6 (>= 2.4), libpq5, debconf (>= 0.5) | debconf-2.0, rsyslog (= 8.24.0-1), dbconfig-common, ucf Recommends: postgresql-client Suggests: postgresql Section: admin Priority: extra Homepage: http://www.rsyslog.com/ Description: PostgreSQL output plugin for rsyslog This plugin allows rsyslog to write syslog messages into a PostgreSQL database.
Display deb package contents.
$ dpkg --contents rsyslog-pgsql_8.24.0-1_amd64.deb
drwxr-xr-x root/root 0 2017-01-18 22:14 ./ drwxr-xr-x root/root 0 2017-01-18 22:14 ./usr/ drwxr-xr-x root/root 0 2017-01-18 22:14 ./usr/lib/ drwxr-xr-x root/root 0 2017-01-18 22:14 ./usr/lib/x86_64-linux-gnu/ drwxr-xr-x root/root 0 2017-01-18 22:14 ./usr/lib/x86_64-linux-gnu/rsyslog/ -rw-r--r-- root/root 14360 2017-01-18 22:14 ./usr/lib/x86_64-linux-gnu/rsyslog/ompgsql.so drwxr-xr-x root/root 0 2017-01-18 22:14 ./usr/share/ drwxr-xr-x root/root 0 2017-01-18 22:14 ./usr/share/dbconfig-common/ drwxr-xr-x root/root 0 2017-01-18 22:14 ./usr/share/dbconfig-common/data/ drwxr-xr-x root/root 0 2017-01-18 22:14 ./usr/share/dbconfig-common/data/rsyslog-pgsql/ drwxr-xr-x root/root 0 2017-01-18 22:14 ./usr/share/dbconfig-common/data/rsyslog-pgsql/install/ -rw-r--r-- root/root 1006 2017-01-18 22:14 ./usr/share/dbconfig-common/data/rsyslog-pgsql/install/pgsql drwxr-xr-x root/root 0 2017-01-18 22:14 ./usr/share/doc/ drwxr-xr-x root/root 0 2017-01-18 22:14 ./usr/share/doc/rsyslog-pgsql/ -rw-r--r-- root/root 438 2017-01-18 22:14 ./usr/share/doc/rsyslog-pgsql/NEWS.Debian.gz -rw-r--r-- root/root 15362 2017-01-18 22:14 ./usr/share/doc/rsyslog-pgsql/changelog.Debian.gz -rw-r--r-- root/root 163021 2017-01-10 09:09 ./usr/share/doc/rsyslog-pgsql/changelog.gz -rw-r--r-- root/root 4454 2017-01-18 22:14 ./usr/share/doc/rsyslog-pgsql/copyright drwxr-xr-x root/root 0 2017-01-18 22:14 ./usr/share/rsyslog-pgsql/ -rw-r--r-- root/root 152 2017-01-18 22:14 ./usr/share/rsyslog-pgsql/rsyslog-pgsql.conf.template
Simple as that.