There are several online PDF readers that you can integrate into your own website:
Mozilla PDF.js: An open-source PDF reader built by Mozilla. It can be easily integrated into your website using JavaScript. You can find more information on how to use PDF.js here: https://mozilla.github.io/pdf.js/
Google Docs Viewer: Google provides a free online PDF viewer that can be embedded into your website using an iframe. You can find more information on how to use the Google Docs Viewer here: https://docs.google.com/viewer
Adobe Acrobat Reader: Adobe provides a free online PDF reader that can be embedded into your website using JavaScript. You can find more information on how to use Adobe Acrobat Reader here: https://www.adobe.com/products/acrobat/pdf-reader.html
Foxit PDF Reader: Foxit provides a free online PDF reader that can be embedded into your website using JavaScript. You can find more information on how to use Foxit PDF Reader here: https://www.foxitsoftware.com/pdf-reader/
FlippingBook: FlippingBook provides a paid PDF reader that can be embedded into your website using JavaScript. You can find more information on how to use FlippingBook here: https://flippingbook.com/online-pdf-reader
You can choose the best option for your needs based on the features, cost, and ease of integration that you require.