Have we sent spacecrafts to Pluto?

Yes! NASA's New Horizons spacecraft did a fly-by of Pluto in 2015.

New Horizons launched on Jan. 19, 2006. It swung past Jupiter for a gravity boost and scientific studies in February 2007, and conducted a six-month-long reconnaissance flyby study of Pluto and its moons in summer 2015.

Among it's discoveries (from NASA's Solar System Exploration website):

New Horizons was used to conclusively answer one of the most basic mysteries about Pluto: its size. Mission scientists concluded that Pluto is about 1,470 miles (2,370 kilometers) in diameter, slightly larger than prior estimates. Its moon Charon was confirmed to be about 750 miles (1,208 kilometers) in diameter.

Besides collecting data on Pluto and Charon (the Charon flyby was at about 17,900 miles or 28,800 kilometers), New Horizons also observed Pluto’s other satellites, Nix, Hydra, Kerberos and Styx.

Data from New Horizons clearly indicated that Pluto and its satellites were far more complex than imagined, and scientists were particularly surprised by the degree of current activity on Pluto’s surface. The atmospheric haze and lower than predicted atmospheric escape rate forced scientists to fundamentally revise earlier models of the system.

Pluto, in fact, displays evidence of vast changes in atmospheric pressure and possibly had running or standing liquid volatiles on its surface in the past. There are hints that Pluto could have an internal water-ice ocean today.

Stunning photographs showed a vast heart-shaped nitrogen glacier (named Sputnik Planitia for Sputnik 1, Earth’s first artificial satellite) on the surface. It’s about 600-miles wide (1,000 kilometers), undoubtedly the largest known glacier in the solar system.

On Charon, images showed an enormous equatorial extension tectonic belt, suggesting a long-past water-ice ocean.

New Horizon's continues its voyage out into the solar system on an extended mission. On New Year's Day 2019, New Horizons flew by the Kuiper Belt Object 2014 MU69. In November 2019, this object was officially renamed Arrokoth, a Native American term meaning “sky” in the Powhatan/Algonquian language.

In April 2021, New Horizons crossed a milestone, reaching a distance of 50 times as far from the Sun as Earth.