Welcome to the AtoM community!
When a multi-page PDF is uploaded, AtoM will generate a preview of the first page. However, if users click on the preview, the full PDF will open in a new tab, using the browser's built-in PDF reader to display the content. Here is an example of a description with a 4-page PDF in our demo site:
It's also possible to tell AtoM to use a different page from the PDF when generating the derivatives. This is especially useful if your institution adds a common cover page to all PDFs, to ensure that users can see the actual content in the preview and not just the same cover page for every PDF. The World Bank Group Archives does this regularly: here is an example of a description with a PDF of 146 pages, showing the third page in the preview since the first 2 pages are cover pages used in many World Bank PDFs:
For more on this setting, see:
You can read more general information on managing digital objects in AtoM here: