bootstrap4.css
.form-control-plaintext {
  display: block;
  width: 100%;
  padding-top: 0.375rem;
  padding-bottom: 0.375rem;
  margin-bottom: 0;
  line-height: 1.5;
  color: #212529;
  background-color: transparent;
  border: solid transparent;
  border-width: 1px 0;
}
bootstrap4.css
.form-control-plaintext.form-control-sm, .form-control-plaintext.form-control-lg {
  padding-right: 0;
  padding-left: 0;
}
bootstrap4.css
@media (min-width: 576px) {
  .form-inline label {
    display: -ms-flexbox;
    display: flex;
    -ms-flex-align: center;
    align-items: center;
    -ms-flex-pack: center;
    justify-content: center;
    margin-bottom: 0;
  }
  .form-inline .form-group {
    display: -ms-flexbox;
    display: flex;
    -ms-flex: 0 0 auto;
    flex: 0 0 auto;
    -ms-flex-flow: row wrap;
    flex-flow: row wrap;
    -ms-flex-align: center;
    align-items: center;
    margin-bottom: 0;
  }
  .form-inline .form-control {
    display: inline-block;
    width: auto;
    vertical-align: middle;
  }
  .form-inline .form-control-plaintext {
    display: inline-block;
  }
  .form-inline .input-group,
  .form-inline .custom-select {
    width: auto;
  }
  .form-inline .form-check {
    display: -ms-flexbox;
  
bootstrap4.css
.input-group > .form-control,
.input-group > .form-control-plaintext,
.input-group > .custom-select,
.input-group > .custom-file {
  position: relative;
  -ms-flex: 1 1 auto;
  flex: 1 1 auto;
  width: 1%;
  margin-bottom: 0;
}
bootstrap4.css
.input-group > .form-control + .form-control,
.input-group > .form-control + .custom-select,
.input-group > .form-control + .custom-file,
.input-group > .form-control-plaintext + .form-control,
.input-group > .form-control-plaintext + .custom-select,
.input-group > .form-control-plaintext + .custom-file,
.input-group > .custom-select + .form-control,
.input-group > .custom-select + .custom-select,
.input-group > .custom-select + .custom-file,
.input-group > .custom-file + .form-control,
.input-group > .custom-file + .custom-select,
.input-group > .custom-file + .custom-file {
  margin-left: -1px;
}
■フォーム:form-group:コンポーネント:読み取り専用テキストの枠を非表示にする

  <form>
    <div class="form-group row">
      <label for="staticEmail" class="col-sm-2 col-form-label">メールアドレス</label>
      <div class="col-sm-10">
        <input type="text" class="form-control-plaintext" readonly id="staticEmail" value="email@example.com">
      </div>
    </div>
    <div class="form-group row">
      <label for="inputPassword" class="col-sm-2 col-form-label">パスワード</label>
      <div class="col-sm-10">
        <input type="password" class="form-control" id="inputPassword" placeholder="パスワードを入力">
      </div>
    </div>
  </form>