Align button to the right

You can also use like below code.

<button style="position: absolute; right: 0;">Button</button>

<div class="container-fluid">
  <div class="row">
    <h3 class="one">Text</h3>
    <button class="btn btn-secondary ml-auto">Button</button>
  </div>
</div>

.ml-auto is Bootstraph 4's non-flexbox way of aligning things.

Bootstrap 4 uses .float-right as opposed to .pull-right in Bootstrap 3. Also, don't forget to properly nest your rows with columns.

<div class="row">
    <div class="col-lg-12">
        <h3 class="one">Text</h3>
        <button class="btn btn-secondary float-right">Button</button>
    </div>
</div>