That's because he's a user (he/she no sex intended).
In order to use installpkg or pkgtool you have to be root, it's in /sbin
Also, I wouldn't use pkgtool or installpkg on it because it's not a slackpack but rather a standard tarball (likely anway).
Where filename.tar.gz is the name of the file.
Then you will see if it is indeed a slackpack. If not, you should follow these instructions:
And/or these instructions:
To install and use it.
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