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.

this.data = parameters.data;
    this.layer = parameters.layer;
    this.page = parameters.page;
    this.viewport = parameters.viewport;
    this.linkService = parameters.linkService;
    this.downloadManager = parameters.downloadManager;
    this.imageResourcesPath = parameters.imageResourcesPath;
    this.renderForms = parameters.renderForms;
    this.svgFactory = parameters.svgFactory;
    this.annotationStorage = parameters.annotationStorage;
    this.enableScripting = parameters.enableScripting;
    this.hasJSActions = parameters.hasJSActions;
    this._fieldObjects = parameters.fieldObjects;
    this._mouseState = parameters.mouseState;
    if (isRenderable) {
      this.container = this._createContainer(ignoreBorder);
    }
    if (createQuadrilaterals) {
      this.quadrilaterals = this._createQuadrilaterals(ignoreBorder);
    }
  }
  /**
   * Create an empty container for the annotation's HTML element.
   *
   * @private
   * @param {boolean} ignoreBorder
   * @memberof AnnotationElement
   * @returns {HTMLElement} A section element.
   */
  _createContainer(ignoreBorder = false) {