LaTeX has several compilers, each with different capabilities and output. The most common are pdflatex, xelatex, and lualatex. They all read .tex files and produce output (PDF by default).

pdflatex is the standard compiler. It's fast, stable, and widely supported. It directly produces PDF output and is best for most documents.

pdflatex document.tex

pdflatex uses traditional TeX fonts (Computer Modern) and font encoding (8-bit). Non-Latin characters and modern font formats require extra setup. It's the most conservative but most portable choice.

xelatex uses Unicode natively and supports modern system fonts (TrueType, OpenType). Better for non-Latin scripts, custom fonts, and internationalization.

xelatex document.tex

The .tex file remains the same; just compile with xelatex instead. You can use any font installed on your system:

\usepackage{fontspec}
\setmainfont{DejaVu Serif}
\setsansfont{DejaVu Sans}

xelatex is slower than pdflatex but handles modern fonts and Unicode naturally.

lualatex is like xelatex but uses Lua scripting for extensibility. It's newer and less widely used but powerful for complex document generation.

lualatex document.tex

Comparison:

When to use each: Start with pdflatex for simple documents. If you need custom fonts or non-Latin scripts, switch to xelatex. Use lualatex only if you need Lua scripting.

Output format: All three produce PDF by default. To generate DVI (device-independent format) instead, use pdftex -output-format=dvi document.tex (rare nowadays). PostScript output (dvips) is mostly obsolete.

Compilation chain with BibTeX:

pdflatex main.tex      # first pass
bibtex main            # extract citations
pdflatex main.tex      # second pass
pdflatex main.tex      # third pass (resolve references)

The same process works for all three compilers. BibTeX works the same way regardless.

Font caching: xelatex and lualatex cache fonts. Clear the cache if you install new fonts: rm -rf ~/.cache/fontconfig (Linux), then recompile.