Following a brief stint in the pathology department at the Rudolfstiftung Hospital, he joined the Second Medical University Clinic (Zweite Medizinische Universitätsklinik) of the City of Vienna, under the direction of his later mentor, Karl Fellinger (1904–2000).

[4] In 1956/57, Höfer spent time at the University of California, San Francisco and Berkeley as a Fulbright Scholar, followed by a research stay at the Medical School in London in 1961.

As a member of the building commission for the "New General Hospital of Vienna", Höfer played a crucial role in designing one of Europe's best-equipped university clinics for nuclear medicine and oversaw its move to the new facility in 1992.

Alongside Karl Fellinger and Herbert Vetter, he founded the international conference series "Radioactive Isotopes in Clinical Medicine and Research" in Bad Gastein, which he co-organized from 1954 to 1993.

A notable feature of the symposium was the regular participation of scientists from Eastern Europe, which was facilitated by Austria’s neutral status during the Cold War.

[4] Additionally, on behalf of the International Atomic Energy Agency, Höfer contributed to setting up isotope units in Tunis, Cairo, Bucharest, Tirana, Syria, and Sudan.

[8] On the occasion of his 90th birthday, a commemorative plaque was installed at the Vienna University Clinic for Nuclear Medicine, which at the time was led by his former student, Helmut Sinzinger.