View a PDF file in HTML not to download it

I have a very simple pure html file in which I have many PDF files. I have link it like this:

<a href="pdffile.pdf"> PDF 1 here </a>

When I click the link, the PDF file is downaloaded and viewed in the native Reader program. I want it to open in another window of the browser, and read it there, rather then saving a copy manually to my computer and opening it.