.modal-content {
        width: 850px;
        text-align: center;
        vertical-align: middle;
    }

<div class="modal fade in" aria-hidden="false" id="displayDocumentModal">
            @*<div class="modal-backdrop"></div>*@
            @*<div class="modal-dialog">*@
                <div class="modal-content">
                    <div class="well">
                        <div class="panel panel-inverse">
                            <div class="panel-heading m-b-10">
                                <div class="panel-heading-btn">
                                    <a class="btn btn-xs btn-icon btn-circle btn-danger" data-dismiss="modal"><i class="fa fa-time</i></a>
                                </div>
                                <h4 class="panel-title text-left">Document Modification</h4>
                            </div>
                            <div>
                                <form id="form1">
                                    <div style="width: 1100px; display: inline;">
                                        <div id="_toolbar1" style="width: 1000px; display: inline; white-space: nowrap;"></div>
                                        @*<div id="_containerThumbs" style="width: 180px; height: 600px; display: inline-block;"></div>*@
                                        <div id="_containerViewer" style="width: 810px; height: 600px; display: inline-block;"></div>
                                    </div>
                                </form>
                            </div>
                        </div>
                    </div>
                </div>
            </div>
        </div>