Pimco, one of the world’s largest fixed-income investors, has been ramping up its commercial real-estate holdings at the same time that historically low interest rates have undercut bond returns. The firm, which is officially known as Pacific Investment Management Co. and has $2.2 trillion under management, has been seeking higher yields than those offered by investment-grade corporate bonds by buying hotels, office buildings and other property types that have lost value during the Covid-19 pandemic.