<div id="thePdfContainer" class="text-center">
    <embed src="https://www.setasign.com/files/demo-files/pdfs/lenstown/Fact-Sheet.pdf" width="300" height="300" type='application/pdf' id="thePdf">
</div>

<div class="button">
    <button class="btn-info" type="button" onclick="switchPdf();">Search</button>
</div>

function switchPdf() {
    var fileA = 'https://www.setasign.com/files/demo-files/pdfs/lenstown/Fact-Sheet.pdf',
        fileB = 'https://www.setasign.com/files/demo-files/pdfs/tektown/Fact-Sheet.pdf',
        container = document.getElementById('thePdfContainer'),
        elem = document.getElementById('thePdf');

    var newFile = (elem.src === fileA) ? fileB : fileA;

    container.innerHTML = '<embed src="' + newFile + '" width="300" height="300" type="application/pdf" id="thePdf">';

    console.log(container.innerHTML);
}