data: URIs are deprecated for generating content. Use object URLs and Blobs (https://developer.mozilla.org/en-US/docs/DOM/Blob). If you want to force saving the file to a disk use <a download="[filename]">
Just as annoyingly, IE10 has createObjectURL too, but only allows the created URLs to be used for <img>, <audio> and <video>. To save a blob, you have to use something ms-prefixed instead, and this doesn't allow inline PDF viewing.