In 1897, he went to Europe, studying at the School of Arts and Crafts in Aarau, Switzerland.
[2] Rojas returned to Paraguay and from 1900 to 1915 was curator of the "Herbario Hassleriano", the herbarium collection of Swiss botanist, Emil Hassler.
In 1906 he participated in an expedition to the Pilcomayo region, the collections from which formed the basis of Hassler's 1909 publication, Flora Pilcomayensis.
Plantae a custode herbarii mei T. Rojas in Chaco septentrionali lectae, the series entitled Comision argentino-paraguaya de limites 1906.
In 1916 he was appointed head of the herbarium and museum of natural history of the Botanical Garden and Zoo of Asunción where he worked for many years.