Go through this article : Convert HTML/CSS Content to a Sleek Multiple Page PDF File Using jsPDF JavaScript library. The provided script allows you to convert any HTML element to PDF. I modified the generate() function slightly so that it takes any HTML element id name and export it as PDF file:

generate = function(doc)
{
	var pdf = new jsPDF('p', 'pt', 'a4');
	pdf.setFontSize(18);
	pdf.fromHTML(document.getElementById(doc), 
		margins.left, // x coord
		margins.top,
		{
			// y coord
			width: margins.width// max width of content on PDF
		},function(dispose) {
			headerFooterFormatting(pdf, pdf.internal.getNumberOfPages());
		}, 
		margins);
		
	var iframe = document.createElement('iframe');
	iframe.setAttribute('style','position:absolute;right:0; top:0; bottom:0; height:100%; width:650px; padding:20px;');
	document.body.appendChild(iframe);
	
	iframe.src = pdf.output('datauristring');
};

It works 100% on Chrome but Im not sure about other browsers.

Add jspdf.plugin.standard_fonts_metrics.js.

you could just use the HTML5 download attribute. E.G download or if you need the javascript engine to do it.

let fileHref = baseLocation + '/excelexports/' + fileName;
var anchor = document.createElement('a');
anchor.setAttribute("download", true);
anchor.setAttribute("href", fileHref);
anchor.click();

If your using a click to run this javascript you can even pass though the event to help identify your download as a user action to more intrusive popup blockers.

someElem.addEventListener('click', function(evt){
    let fileHref = baseLocation + '/excelexports/' + fileName;
    var anchor = document.createElement('a');
    anchor.setAttribute("download", true);
    anchor.setAttribute("href", fileHref);
    anchor.dispatchEvent(evt);
});

source: https://www.w3schools.com/tags/att_a_download.asp

If you want to download the file based on a link, you can add a custom lightning button and then add below code that should download the file for you.

<lightning-button variant="brand" label="Download" title="Primary action" onclick={handleClick} class="slds-m-left_x-small"></lightning-button>

in your JS :

handleClick(event){
    let downloadLink = document.createElement("a");
                downloadLink.setAttribute("type", "hidden");
                downloadLink.href = "data:application/octet-stream;base64,"+this.pdfData; // PDF base64Data
                downloadLink.download = "filename.pdf";//modify as you need
                document.body.appendChild(downloadLink);
                downloadLink.click();
                downloadLink.remove();
}

this is what I could make it work from StachExchange only, I am having hard time finding that thread to link here.

Also, for Print you dont need to do anything differently, using cmd + p in mac works for me to get print pop up.

The general approach I use for such situations is to start poking around in the Developer tools of any browser and finding the Network tab.

Sort by file size to find the largest listing of the PDF file, as this is most likely to be the complete file without missing pages. If you don't see it, try reloading the page. From there, try these in order, from easiest to most annoying.

Method 1: If you're really lucky there will be an accessible URL for the PDF you can download directly. Just right click and open the file in a few tab, then you can save it.

Method 2: Copy the cUrl command and pipe that to a file. In theory this may be possible from any command prompt but I've had the best luck with Linux/WSL.

Method 3: Save as HAR with content, and use something like har-extractor to extract the PDF.

To print html from iframe, you need to get content from iframe. Source code to get content from iframe (I got from this):

function getFrameContents() {
    var iFrame = document.getElementById('frame');
    var iFrameBody;
    if (iFrame.contentDocument) { // FF
        iFrameBody = iFrame.contentDocument.getElementsByTagName('body')[0];
    } else if (iFrame.contentWindow) { // IE
        iFrameBody = iFrame.contentWindow.document.getElementsByTagName('body')[0];
    }
    //alert(iFrameBody.innerHTML);
    return iFrameBody.innerHTML
}

So you replace:

source = $('#frame')[0]

with

source = getFrameContents();

or simple with jQuery:

source = $("#frame").contents().find('body')[0];

However, there is still issue about CORS (Cross-Origin Resource Sharing). To solve it, you can create web server and put you html code and iframe src in there and see how it work.

• I don't understand why there's brackets around an attribute: [src] If you don't already know: Don't do that.

• <iframe> doesn't have type as a valid attribute, but type does work for <iframe>'s sister tags <object> and <embed>.

The following Demo does not function on SO due to their restrictive sandbox. Go to this Plunker to see a functional Demo. Source PDF courtesy of PDFObject

It looks like Plunker no longer runs embeded content anymore, so if you want to review a functioning demo, simply copy and paste the entire code in any text editor (Notepad, Notepad++, etc.) and save as an HTML file (.html file extension).

<!DOCTYPE html>
<html>

<head>
  <style>
    * {
      margin: 0;
      padding: 0;
    }
    
    figure {
      display: table;
      border: 3px ridge grey;
      position: relative;
      width: 96vw;
      min-height: 250px;
      height: auto;
      margin: 0 auto 35px;
    }
    
    figcaption {
      border: 3px ridge grey;
      text-align: center;
      font: 900 20px/1.5 Verdana;
      padding: 0 0 8px 0;
      background: rgba(51, 51, 51, 0.3);
      color: #fff;
    }
    
    iframe,
    object,
    embed {
      overflow: hidden;
      position: absolute;
    }
  </style>
</head>

<body>

  <figure>
    <figcaption>IFRAME</figcaption>
    <iframe src="https://pdfobject.com/pdf/sample-3pp.pdf#page=1" class="frameSet" frameborder="0" allowfullscreen width="100%" height="100%"></iframe>
  </figure>

  <figure>
    <figcaption>OBJECT</figcaption>
    <object data="https://pdfobject.com/pdf/sample-3pp.pdf#page=2" class="objectSet" type="application/pdf" width="100%" height="100%"></object>
  </figure>

  <figure>
    <figcaption>EMBED</figcaption>
    <embed src="https://pdfobject.com/pdf/sample-3pp.pdf#page=3" class="embedSet" type="application/pdf" width="100%" height="100%">
  </figure>

</body>


</html>

I have struggled a bit to find a solution that works for both IE and Chrome. This works for me:

$(function() {
    var ua = window.navigator.userAgent;
    var msie = ua.indexOf('MSIE ');
    var trident = ua.indexOf('Trident/');
    var edge = ua.indexOf('Edge/');
    var url = '/url/to/file.pdf';
    var pdf ='';
    var style = 'position:fixed; top:0px; left:0px; bottom:0px; right:0px; width:100%; height:100%; border:none; margin:0; padding:0; overflow:hidden;';

    if(msie > 0 || trident > 0 || edge > 0){
        pdf = '<object data="' + url + '" name="print_frame" id="print_frame" style="' + style + '" type="application/pdf">';
    }
    else{
        pdf ='<iframe src="' + url + '" name="print_frame" id="print_frame" style="' + style + '"></iframe>';
    }

    $(document.body).append(pdf);

    setTimeout(function(){
        window.frames["print_frame"].focus();
        window.frames["print_frame"].print();
    },2000);
});

...cheers.