Support a document loader using the MarkItDown library

[Simon-Stone]

Checked

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Feature request

Implement a document loader class that uses the MarkItDown library to convert files into Markdown. From the MarkItDown README:

MarkItDown is a utility for converting various files to Markdown (e.g., for indexing, text analysis, etc). It supports:

PDF
PowerPoint
Word
Excel
Images (EXIF metadata and OCR)
Audio (EXIF metadata and speech transcription)
HTML
Text-based formats (CSV, JSON, XML)
ZIP files (iterates over contents)

Motivation

Formatting and layout of documents can convey important context information to the human reader. Using text-based markup languages like Markdown can be very helpful to preserve this information in the text-only representation passed to Large Language Models. The Markitdown library is a great, versatile tool to easily convert different kinds of files into a Markdown representation.

Proposal

I propose a simple MarkitdownLoader class derived from BaseLoader using markitdown.MarkItDown under the hood (composition pattern).

I will try my hand at this and offer a PR soon.

[Simon-Stone]

I've started working on PR #28960 but I'm running into the challenge that MarkItDown requires Python 3.10+, but langchain_community still supports 3.9.

Is there any precedent for how to deal with this? Or am I just SOL until the powers that be decide to drop support for 3.9?