Provided you have an up to date acro
you can define a definite article and commands that make use of it. All you then have to do is define the acronym accordingly:
\documentclass{article} \usepackage{acro} \DeclareAcroArticle{definite}{the} \DeclareAcroEnding{possessive}{'s}{'s} \NewAcroCommand\dac{m}{\acrodefinite\UseAcroTemplate{first}{#1}} \NewAcroCommand\Dac{m}{\acroupper\acrodefinite\UseAcroTemplate{first}{#1}} \NewAcroCommand\Dacg{m}{% \acroupper \acrodefinite \acropossessive \UseAcroTemplate{first}{#1}% } \DeclareAcronym{css}{ short = CSS , long = Centre for Spaghetti Studies , short-definite = \nospace , long-possessive = ' } \begin{document} Bob hails from \dac{css}. \par Bob hails from \dac{css}. \acreset{css} \Dacg{css} mandate is broad. \par \Dacg{css} mandate is broad. \acreset{css} \Dac{css} scientists eat well. \par \Dac{css} scientists eat well. \par \end{document}