Hi @Ashish Ghatak ,
First add the Web Part of the Document Library to the left panel to display the required document library and Site Pages, and then add the Web Part of the File viewer to the right panel for optional display.
- left panel: Add 'Document library' Web Part->Select document library to add to this page.
2.right panel: Add 'File viewer' Web Part->Cancel->Edit web part->More options->Connect to source->Submit for approval
3.Below is what we get after the configuration. Please let me know if you have any additional requirements or concerns about the set up I mentioned above.
Please note: site pages library is not supported
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