Attach (recommended) or Link to PDF file [here:] Can't see how to attach a pdf here, but it is simple to create. Add a form object textbox to a pdf and make sure the option for "Multiline" is true.

Steps to reproduce the problem:
1.  Open a document with a Textbox that is set to Multiline.
2. Attempt to hit the Enter key to go to a new line.

What is the expected behavior? The cursor goes to a new line.

What went wrong? It does not go to a new line.

Link to a viewer: It can be reproduced on mozilla.github.io/pdf.js

I corrected the issue by altering the pdf.js file like this
element.addEventListener("keydown", event => { 
[...]
--} else if (event.key === "Enter") {
++ } else if (event.key === "Enter" && !this.data.multiLine) {

Our initial testing is coming through clean, and hopefully something like this code can be committed to the project in the future.

constructor(parameters) {
    super(parameters, { isRenderable: parameters.renderForms });
  }
  render() {
    this.container.className = "choiceWidgetAnnotation";
    const storage = this.annotationStorage;
    const id = this.data.id;
    const storedData = storage.getValue(id, {
      value: this.data.fieldValue,
    });
    const selectElement = document.createElement("select");
    GetElementsByNameSet.add(selectElement);
    selectElement.setAttribute("data-element-id", id);
    selectElement.disabled = this.data.readOnly;
    this._setRequired(selectElement, this.data.required);
    selectElement.name = this.data.fieldName;
    selectElement.tabIndex = DEFAULT_TAB_INDEX;
    let addAnEmptyEntry = this.data.combo && this.data.options.length > 0;
    if (!this.data.combo) {
      
      selectElement.size = this.data.options.length;
      if (this.data.multiSelect) {
        selectElement.multiple = true;
      }
    }
    selectElement.addEventListener("resetform", event => {
      const defaultValue = this.data.defaultFieldValue;
      for (const option of selectElement.options) {
        option.selected = option.value === defaultValue;