Microsoft Copilot 365 Personal Premium limits

In my Copilot Notebook, I deliberately loaded 20 PDF files in order to test Copilot’s grounding behavior across the full set of available references. At the time this testing setup was created, 20 references represented the effective grounding limit described for Copilot Notebooks, meaning that these references were expected to form the source base used by Copilot when generating grounded responses.

The references consisted of fully functional, original academic textbooks containing relevant and up-to-date scientific information, mostly published within the last ten years.

Importantly, the sources do not differ from one another in terms of accessibility, file type, availability, or how they were added to the notebook. They are all PDF files, they are all available in the same environment, and there is no obvious difference in access conditions that would explain why some are consistently used while others are repeatedly treated as inaccessible, unavailable, summarized, or skipped.

The purpose of the test was therefore not simply to see whether Copilot could access 20 files, but whether it could actually ground its answers in the complete reference set when explicitly instructed to analyze all available sources.

Despite this, in approximately 99.9% of my tests, Copilot appears to ground its responses in only 3 to 5 of the 20 available references, often repeatedly using the same documents.

When I ask what happened to the remaining sources, Copilot gives different explanations.

Sometimes it says that it does not have access to certain files.

Sometimes it says that it only received a summary of the file.

Sometimes it says that a step involved in retrieving or processing the information failed.

The way Copilot explains this often makes it sound as if access to the uploaded files depends on some external or intermediate system, rather than being something Copilot itself can directly control.

This is difficult to understand from a user perspective because the files are already uploaded into the Copilot environment and were specifically provided as source material for analysis.

The practical result is that a task explicitly requesting analysis of 20 sources often produces an answer based on only 3 to 5 of them.

For academic or research use, this is a serious limitation. If 15 to 17 out of 20 carefully selected sources are not actually examined, then the final synthesis cannot realistically represent the full source base.

This also creates uncertainty about what Copilot means when it claims to have used the provided materials.

My question to Microsoft is:

Is there a technical limit on how much information Copilot can actually retrieve, open, and analyze from uploaded files during a single task or session?

If such a limit exists, what is that limit?

And why, when 20 valid PDF sources are uploaded and Copilot is explicitly instructed to analyze all of them, does it so often appear to open only 3 to 5 files, while describing the others as inaccessible, summarized, or unavailable because some retrieval step failed?