Para tener el papel en mis manos, imprimo a. un diseño b. una copia impresa

una copia impresa translates into a hard copy and is a printed version on paper of data held in a computer. So, if you want to get a paper with information that is in your computer, you need to print a copy. Since copia impresa is given in feminine singular form, we need to use the feminine singular definite article, which is una.