With the following setup, you can just type these characters normally, and the copy-paste text in the pdf (the OCR layer) will be correct, too. Your source .tex document should be encoded in UTF8, of course, or you could use latin1
, or some other input encoding that includes the characters you desire and is listed in the inputenc
documentation.
% !TEX encoding = UTF-8 Unicode
\documentclass{article}
\usepackage{lmodern}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\begin{document}
áéíóú àìèòù âêîôû
\end{document}

I think this setup should work for all languages with Latin script when using pdfLaTeX. Another option would be XeLaTeX or LuaLaTeX, which support Unicode natively.
pdfLaTeX’s UTF8 isn’t actually the full Unicode set, but here’s a more expansive collection of lower case letters that work:
áćéíĺńóŕśúýź àèìòù
âêîôû äëïöüÿ ąę ăğ
ãñõ æœ åů čěňřšž çşţ
ð đłø ďľť ı ij ŋ őű ß þ ż

The line
% !TEX encoding = UTF-8 Unicode
is supposed to stress the fact that your .tex file needs to be encoded in UTF8. It is automatically read and understood by a few editors, including TeXworks and TeXShop; un other editors, it doesn’t do any harm since it’s just a comment. See When and why should I use % !TEX TS-program and % !TEX encoding?.
lmodern
loads the Latin Modern fonts, which look mostly the same as the standard TeX Computer Modern fonts, but has some minor advantages in my opinion, including the placement of the acute and grave accents. See Latin Modern vs cm-super? (my answer there demonstrates the accents).
Further reading
inputenc
and fontenc
XeLaTeX and LuaLaTeX