Robinhood Markets Inc. agreed to buy TradePMR, a custodial and portfolio management platform for registered investment advisors, as the online brokerage seeks to target a wider swath of wealthier investors. The deal — for about $300 million in cash and stock — is expected to close in the first half of next year, Robinhood said in a statement. Through the acquisition, TradePMR’s registered investment advisors will be able to access Robinhood’s clients, who will be able to easily connect with RIAs...