Since WordPress 5.8 it is no longer necessary to install any plugin or use an external service to display PDF files directly on your website.
With the file block you have this functionality natively, and active by default.
Even if you search for “PDF” in the block inserter you will be shown the file block.
Once the block has been added, just choose the PDF file and it will be displayed with an integrated viewer, of which you can modify settings such as the height, whether it will have a download button for the file, or where the text link will link to.
And that’s it. You will be able to fully preview the PDF from your posts and pages.