Complex sentence: UCSC Archives Baer soon found a well-paying but dull job in the advertising office of the Chicago department store Marshall Field's, but soon apprenticed as a low-paid menial assistant, at a greatly reduced salary, to a Michigan Avenue commercial photography company.
Split into simpler sentences: UCSC Archives Baer soon found a dull but well-paying job in the advertising office of the Chicago department store Marshall Field's. Dissatisfied, he apprenticed as a low-paid menial assistant, at a greatly reduced salary, to a Michigan Avenue commercial photography company.