How to set up Chromium Based Browser to Open PDF Files Externally.
2. Click on the Menu icon in the top-right corner of the Window.
3. Click Settings.
4. Scroll down to the bottom of the Settings window and click Advanced.
5. In the Privacy and security section, click Site Settings.
6. Scroll down and click the PDF documents option.
7. Change the “Download PDF files instead of automatically opening them in Chromium based browser” option from the off position (grey) to the on position (blue).
8. Close the Settings tab and now any PDF should be opened in your locally installed PDF viewer.