How to get "LaTeX" symbol in document

You simply type \LaTeX. One problem with this is that if you type it a lot of times in your text you will need to type \LaTeX\␣¹ (i.e., followed by \ and an actual space) to force a space after it.

Also personally I find the capitalization of L and T leads to typing errors, so I redefine the command as follows:

\newcommand{\latex}{\LaTeX\xspace}
\newcommand{\tex}{\TeX\xspace}

\xspace is from the xspace package. Additionaly, writing \LaTeX{} adds the space after.

---

^{¹ ␣ is used here to represent a normal space "", which wouldn’t show up at the end of Markdown code markup.}

There is also the hologo package for typesetting TeX-related logos:

\hologo{LaTeX}
\Hologo{LaTeX}  % to be used at the beginning of a sentence (no difference in this case)

While the syntax is a bit more verbose, it has the advantages that you don't have to think about trailing spaces and that it works correctly inside PDF bookmarks.

Use the following

% !TEX encoding = UTF-8 Unicode
\documentclass[UTF8]{article}
\begin{document}

\LaTeX

\end{document}

you will get

Notice that there are three capital letters in the command.