1. The security architecture of PowerApps requires the PDF Viewer to support only HTTPS links, not HTTP.
2. The Document property must link directly to the PDF file. Server redirects or HTML views of the document aren't supported.
3. The server that hosts the document must not require authentication.
4. You may not be able to view a PDF document in your app if the document resides on a server that has restrictive cross-origin resource sharing (CORS) settings. To resolve this issue, the server that hosts PDF documents must permit cross-origin requests from powerapps.com.
Please check if the PDF files could not be opened correctly within the PDF Viewer control has meet the above requirements.
Community Support Team _ Kris Dai If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.