I have a problem that I have not been able to solve. When I generate my PDF document and want to copy the text to a terminal or a WORD document, the underscores are not copied. In the PDF it does print the underscores (Adobe Acrobat Reader, Foxit Reader) but when I want to copy it from the PDF to another place an empty space appears. I use _, I have also tried \textunderscore. Also, I am using \usepackage[utf8]{inputenc}, \usepackage[T1]{fontenc} and \usepackage{lmodern}. (I have seen that it was solved with \usepackage[T1]{fontenc} but it doesn't work for me.) Could you help me?
This is my preamble:
\documentclass[letterpaper]{article}\usepackage[spanish]{babel}\usepackage[utf8]{inputenc}\usepackage{fancyhdr}\usepackage{authblk}\usepackage{amsfonts}\usepackage[version=3]{mhchem}\usepackage{textgreek}\usepackage{pdflscape} % landscape pages\usepackage[T1]{fontenc}\usepackage{lmodern} % Previene advertencias sobre fuentes no disponibles\usepackage{graphicx}\usepackage[left=3cm,right=2cm,top=2cm,bottom=3cm]{geometry} % Configura los márgenes de página%\usepackage{lineno} %Numeros en las lineas%\linenumbers%Paquete para incluir hipervínculos\usepackage[colorlinks=true, linkcolor = black,urlcolor = blue,citecolor = black,anchorcolor = blue]{hyperref}\usepackage{lipsum}\usepackage{Sweave}\usepackage{multirow}\usepackage[table,xcdraw]{xcolor}\usepackage{array}\usepackage{tabu}\usepackage[labelfont=bf]{caption} %Configura los titulos de las figuras y las tablas en negrita.\usepackage{datetime}\setlength{\parindent}{0pt}%Paquete para el manejo de las unidades en el Sistema Internacional\usepackage{siunitx}\sisetup{mode=text, output-decimal-marker = {,}, per-mode = symbol, qualifier-mode = phrase, qualifier-phrase = { de }, list-units = brackets, range-units = brackets, range-phrase = --}\DeclareSIUnit[number-unit-product = \;] \atmosphere{atm}\DeclareSIUnit[number-unit-product = \;] \pound{lb}\DeclareSIUnit[number-unit-product = \;] \inch{"}\DeclareSIUnit[number-unit-product = \;] \foot{ft}\DeclareSIUnit[number-unit-product = \;] \yard{yd}\DeclareSIUnit[number-unit-product = \;] \mile{mi}\DeclareSIUnit[number-unit-product = \;] \pint{pt}\DeclareSIUnit[number-unit-product = \;] \quart{qt}\DeclareSIUnit[number-unit-product = \;] \flounce{fl-oz}\DeclareSIUnit[number-unit-product = \;] \ounce{oz}\DeclareSIUnit[number-unit-product = \;] \degreeFahrenheit{\SIUnitSymbolDegree F}\DeclareSIUnit[number-unit-product = \;] \degreeRankine{\SIUnitSymbolDegree R}\DeclareSIUnit[number-unit-product = \;] \usgallon{galón}\DeclareSIUnit[number-unit-product = \;] \uma{uma}\DeclareSIUnit[number-unit-product = \;] \ppm{ppm}\DeclareSIUnit[number-unit-product = \;] \eqg{eq-g}\DeclareSIUnit[number-unit-product = \;] \normal{\eqg\per\liter\of{solución}}\DeclareSIUnit[number-unit-product = \;] \molal{\mole\per\kilo\gram\of{solvente}}\addto\captionsspanish{\renewcommand{\tablename}{Tabla}} %Cambia el nombre de cuadros a %tablas