Copilot Agent Cannot Answer Simple Questions Accurately

I created a Copilot Agent at a SharePoint site within our enterprise, and sourced the agent to a document library in that site. I then added our company benefits guide (PDF) to that location. After waiting a day for M365 Search to adequately crawl and index the content, I posed simple questions to the agent on content that is in the guide, such as "what are the company observed holidays" or "what is the company's vesting schedule". Remarkably, the agent repeatedly stated that this information was not in the guide, and it would cite the guide as a reference. Remarkably, it would provide responses stating content that was absolutely not in the guide, such as stating other holidays that were not listed in the guide, or stating a vesting schedule completely not in the guide nor stated anywhere in the guide. On the other hand, I could pose the exact same questions in Copilot Chat, uploading the document to that chat session, and Copilot Chat would provide accurate responses. These experiences are repeatable across every type of PDF-based source for every Copilot agent we have tested.

Nor are Copilot Agents able to accurately return page numbers in PDFs of where it found the content it responded with. For example, a Copilot Agent, sourced to a PDF document in a SharePoint site, consistently returns an inaccurate page number on which it found the beginning of a new section. However, Copilot Chat is able to accurately provide the correct page number, for the exact same question, when that same document is uploaded to the Copilot Chat session.

There are just a few configurable items available when creating a Copilot agent at a SharePoint site. What could be the issue? Is M365 Search not able to adequately read the PDF?