<script type="text/javascript" src="/sites/test/SiteAssets/jquery-2.1.3.min.js"></script>
<script type="text/javascript">
function Custom_AddDocLibMenuItems(m, ctx)
    {
	      $("#where_to_insert").hide();
	      var strDisplayText = "Copy URL document";
	      var url = '';
	      var spans = $('#where_to_insert');
		  spans.text('');
		  function getlist() {
			var requestUri = _spPageContextInfo.webAbsoluteUrl + "/_api/web/lists/getByTitle('Documents')/items?$select=EncodedAbsUrl,FileLeafRef&$filter=Id eq " + currentItemID;
			var requestHeaders = {
			    "accept": "application/json;odata=verbose"
			}
			$.ajax({
			    url: requestUri,
			    type: 'GET',
			    dataType: 'json',
			    headers: requestHeaders,
			    success: function (data) 
			    {        
			       $.each(data.d.results, function(i,result) {
		            var EncodedAbsUrl = result.EncodedAbsUrl;
		            var link = document.createElement('a');
		            if (EncodedAbsUrl != null) {
		                link.href = EncodedAbsUrl;
		              } 
		            var FileLeafRef = result.FileLeafRef;
		            link.textContent = FileLeafRef;
		            var url = document.getElementById('where_to_insert').appendChild(link);
			    copy();
			    });
			       	function copy() {
				      var target = document.getElementById('where_to_insert');
				      var range, select;
				      if (document.createRange) {
				        range = document.createRange();
				        range.selectNode(target)
				        select = window.getSelection();
				        select.removeAllRanges();
				        select.addRange(range);
				        document.execCommand('copy');
				        select.removeAllRanges();
				      } else {
				        range = document.body.createTextRange();
				        range.moveToElementText(target);
				        range.select();
				        document.execCommand('copy');
				      }
				    }
			    },
			    error: function ajaxError(response) {
			        alert(response.status + ' ' + response.statusText);
			    }
			 });
		}
      	CAMOpt(m, strDisplayText, getlist(), strDisplayText.link);
      	CAMSep(m);
      }
</script>
<span id="where_to_insert"></span>"Edit Page to library -> Add a Web Part" -> Category "Media and content" -> Add "Content Editor":

Content Editor "Edit Web Part" add to your JavaScript file:

Check our solution after reloading the page, click to "Open Menu" and again "Open Menu" click item menu "Copy URL document":

Insert your copy into to Outlook messages:

If you hover the mouse over the link, it will see the URL of the document, and if you click, you will go to it by the link.
Happy Coding!
