Adobe Reader is not included in Linux builds as most distributions do have a program capable of rendering pdf documents. For instance, Ubuntu ships with Document Viewer and this will display pdf documents created with TaxCalc. However it is possible that some documents may not be rendered by 3rd party programs correctly.
The latest version of Adobe reader available for Linux is 9.x and Adobe have withdrawn support for it, although at the time of writing it was still available from the following location.
If it is required, download the correct one for your distribution from the above link.
Deb is suitable for Ubuntu, Mint and Debian. RPM covers Redhat, Centos and Fedora.
Installing Adobe Reader on Ubuntu
Installing Adobe Reader on Mint
Other distributions may need to be installed differently.