Angular or React are JS frameworks so once you use them, all of your components should be a Angular or React components. DocumentViewer has a JS part but it also has a server part, it's an ASP.NET component.
Your best bet would be this:
1. Create a page which hosts DocumentViewer in ASP.NET. This page should receive important parameters like the document to display in querystring, e.g. myViewer?doc=SomeIdOrName.pdf
2. In angular, render an <iframe> which points to your page, e.g.
<iframe src="myViewer?doc={{docName}}"The url of your page would probably be a static full url, just like a cdn e.g www.contoso.com/myApp/myViewer?doc so that you can always access it in your JS project.
By the way, very soon we will release a remake version of DocumentViewer and we plan to offer JS part as React, Angular, Vue etc. component. However the JS part will only display PDF files because conversion from other doc formats to PDF is only possible in ASP.NET component.