The pdfViewerEnabled read-only property of the Navigator interface indicates whether the browser supports inline display of PDF files when navigating to them.

If inline viewing is not supported the PDF is downloaded and may then be handled by some external application.

true if the browser can display PDF files inline when navigating to the file (using either an internal viewer or a PDF viewer extension); otherwise false.

To check PDF inline viewing support:

if (!navigator.pdfViewerEnabled) {
  // The browser does not support inline viewing of PDF files.
}