You can not install pdflatex by simply performing command apt-get install pdflatex. It is because the program named pdflatex is actually a file as a part of another package. To install pdflatex in Ubuntu 12.04, 14.04, 16.04, 16.10, and 17.04, perform this command:
sudo apt-get install texlive-latex-base
How to know if a program can not be installed by its name, instead, it should be installed from the package containing it? First, produce an error from APT showing that the program name you invoke is not exist. Second, go to packages.ubuntu.com and search for CONTENT by typing the actual program name.
|Searching for a file as a content of certain package|
|Installing the package containing the actual file|
pdflatex is a program for compiling LaTeX source file (.tex) into PDF file. Many advanced text editors use pdflatex for doing compilation, such as Vim, Emacs, Texmaker, Gummi, and even Scribus.