Limitation on fully retrieving data from large files

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Limitation on fully retrieving data from large files

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Is there an inherent file size limitation for Copliot processing?

This is a project developing facilitator guides from raw audio transcripts of several hours generating between 3000 and 10000 lines of text. At several points throughout the process, Copilot confirmed it could only retrieve fewer than 1000 lines.

Throughout this project I've been working with large source files, transcripts of training sessions. At the beginning it appeared Copilot was returning responses after reviewing the full file but after checking its work, Copilot confirmed that it was only retrieving the first several hundred lines. The prompts were reworked to chunk the source file where appropriate but Copilot still appeared to be able to fully access the file in the initial steps. Even after many iterations, it still didn't fully acknowledge its limited access to the full file. When asked if this was a Copilot limitation, that it can't fully access large files and process them (summarizing, etc.) it was unable to answer.

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Answer 1

Yes. There are practical input and retrieval limits, and the behavior described matches documented Copilot limitations with large files.

For Microsoft 365 Copilot document handling:

For summarizing or referencing content, a general guideline is to keep the total document size to no more than 1.5 million words or 300 pages.
Asking questions about a document works best when the document is under about 7,500 words.
Rewrite works best when the document is under about 3,000 words.
In long files, Copilot can focus on the beginning of the document up to its limits and give less attention to content in the middle. The guidance also notes that large language models tend to prioritize content at the beginning and end of a file.
If a document is longer than the effective limits for the task, Copilot might still respond, but it can effectively behave like it only read the first part.

That explains why a transcript with 3,000 to 10,000 lines could appear partially accessible during early steps but then fail to reliably use the full content for summarization or transformation tasks.

For Copilot Studio-style retrieval behavior, there is also a separate limitation: retrieval is based on returned excerpts/chunks, not end-to-end file reading, and the accepted guidance states that the chunk size can't be increased. In that scenario, removing Markdown is not recommended because headings help retrieval.

Practical approach for long transcripts:

Split the transcript into smaller, self-contained files rather than relying on one large source file.
Summarize in parts by copying or saving chunks into separate documents and processing each section separately.
Keep strong headings/section boundaries so retrieval has clearer anchors.
If the output depends on complete coverage, restate key context in each chunk, because chunks may be retrieved independently.
For tasks that require the entire source to be returned in full, retrieval-based knowledge approaches are not a good fit.

So the short answer is: yes, there is an inherent limitation, but it depends on the Copilot experience and task type. In large transcript workflows, the reliable pattern is to chunk the source intentionally and process it section by section.

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