How do I hide the dropdown of a navbar when a user clicks elsewhere?

There are multiple ways. I kind a like to have separate function variable for clearing previous action:

<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>
.navbar {
  overflow: hidden;
  background-color: #333;
  font-family: Arial, Helvetica, sans-serif;
}

.navbar a {
  float: left;
  font-size: 16px;
  color: white;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;
}

.dropdown {
  float: left;
  overflow: hidden;
}

.dropdown .dropbtn {
  cursor: pointer;
  font-size: 16px;  
  border: none;
  outline: none;
  color: white;
  padding: 14px 16px;
  background-color: inherit;
  font-family: inherit;
  margin: 0;
}

.navbar a:hover, .dropdown:hover .dropbtn, .dropbtn:focus {
  background-color: red;
}

.dropdown-content {
  display: none;
  position: absolute;
  background-color: #f9f9f9;
  min-width: 160px;
  box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
  z-index: 1;
}

.dropdown-content a {
  float: none;
  color: black;
  padding: 12px 16px;
  text-decoration: none;
  display: block;
  text-align: left;
}

.dropdown-content a:hover {
  background-color: #ddd;
}

.show {
  display: block;
}

.wrapper {
  min-width: 800px;
  margin: auto;
}
</style>
</head>
<body>

<div class="wrapper">
<div class="navbar">

  <a href="#home" onclick="myFunction('home')">Company name</a>

  <div class="dropdown">
  <button class="dropbtn" onclick="myFunction(1)">Our Methods
    <i class="fa fa-caret-down"></i>
  </button>
  <div class="dropdown-content" id="myDropdown1">
    <a href="#link">Insurance</a>
    <a href="#link">Divorce</a>
    <a href="#link">Financial Planning</a>
    <a href="#link">Mortgage</a>
    <a href="#link">Stocks</a>
    <a href="#link">Pension</a>
  </div>
  </div>

  <div class="dropdown">
  <button class="dropbtn" onclick="myFunction(2)">Who we are
    <i class="fa fa-caret-down"></i>
  </button>
  <div class="dropdown-content" id="myDropdown2">
    <a href="#link">About the Team</a>
    <a href="#link">Awards</a>
    <a href="#link">Interesting articles</a>
  </div>
  </div>

  <div class="dropdown">
  <button class="dropbtn" onclick="myFunction(3)">Business info
    <i class="fa fa-caret-down"></i>
  </button>
  <div class="dropdown-content" id="myDropdown3">
    <a href="#link">Prices</a>
    <a href="#link">Privacy</a>
    <a href="#link">Methods</a>
  </div>
  </div> 

  <a href="#home" onclick="myFunction('home')">Recommendations</a>

  <div class="dropdown">
  <button class="dropbtn" onclick="myFunction(4)">Advice Evenings
    <i class="fa fa-caret-down"></i>
  </button>
  <div class="dropdown-content" id="myDropdown4">
    <a href="#link">Succesful Pensions</a>
    <a href="#link">Casestudie Pension</a>
    <a href="#link">Business Contacts</a>
  </div>
  </div> 
</div>
</div>

<script>
/* When the user clicks on the button, 
toggle between hiding and showing the dropdown content */
let closeDropdown = function() {

}
function myFunction(num) {
  closeDropdown();
  let el = document.getElementById("myDropdown" + num);  
  if (el) {
    el.classList.toggle("show");
    closeDropdown = function() {
        el.classList.remove("show");
    }
  } else {
    closeDropdown = function() {
    } 
  }
}



</script>
</body>
</html>

The one thing the other answer did not address was how to also hide the dropdowns if one clicks elsewhere on the page. I found that adding the code below solved that issue:

window.onclick = function(event) {
  if (!event.target.matches('.dropbtn')) {
    var dropdowns = document.getElementsByClassName("dropdown-content");
    var i;
    for (i = 0; i < dropdowns.length; i++) {
      var openDropdown = dropdowns[i];
      if (openDropdown.classList.contains('show')) {
        openDropdown.classList.remove('show');
      }
    }
  }
}

There is already css solution given. Given below is my javascript solution. Just replace your javascript code with mine.

<script>
/* When the user clicks on the button, 
toggle between hiding and showing the dropdown content */
let closeDropdown = function() {

}
var oldselection = 0;
function myFunction(num) {
  if(oldselection != 0){
  document.getElementById('myDropdown'+oldselection).classList.remove("show");
// hiding the old dropdown
}
  closeDropdown();
  let el = document.getElementById("myDropdown" + num);  
  if (el) {
    el.classList.toggle("show");
    closeDropdown = function() {
        el.classList.remove("show");
    }
  } else {
    closeDropdown = function() {
    } 
  }
oldselection = num;
}    

</script>

In this code i have jus added 1 variable called "oldselection" and i m storing the previously selected dropdowns "num" value. And during the next selection i m just using the old selected value to hide its associated content.