Working With Files

This is the lesson where Cowork goes from interesting to indispensable. Working with files is what Cowork was built for — and once you see it in action, you’ll wonder how you managed without it.

🔄 Quick Recall: Last lesson, we covered the interface, context windows, and multi-step task structure. Remember the instructions.md trick for persistence? Keep that in mind — we’ll use it here.

Reading Files

The simplest Cowork operation: point it at a file and ask it to read.

Read the file "project-proposal.docx" and give me:
1. A 3-sentence summary
2. The main budget figure
3. Any deadlines mentioned

Cowork handles most common file types — .txt, .md, .csv, .xlsx, .docx, .pdf, .json, and more. It reads the content, not just the filename.

But here’s where it gets interesting. You’re not limited to one file:

Read all the CSV files in this folder.
Tell me which ones have a "revenue" column
and what date range each one covers.

Cowork scans through multiple files, compares them, and gives you a structured answer. Try doing that manually with 20 spreadsheets.

✅ Quick Check: What file types can Cowork read? (Common ones: txt, md, csv, xlsx, docx, pdf, json — plus many others.)

Creating Files

Creating files is where Cowork starts saving you real time. Instead of opening a text editor, formatting a document, and writing from scratch, you describe what you need:

Create a file called "weekly-status.md" with:
- Header: Weekly Status Update — March 19, 2026
- Sections: Completed, In Progress, Blocked, Next Week
- Under Completed, list: shipped new landing page, fixed login bug, updated pricing FAQ
- Leave the other sections with placeholder bullets

Cowork creates the file in your working folder. You can open it in any editor, share it with your team, or refine it further.

More powerful examples:

Create a CSV called "contacts-cleaned.csv".
Read "contacts-raw.csv" and:
- Remove duplicate entries (same email)
- Standardize phone numbers to +1-XXX-XXX-XXXX format
- Flag any rows missing an email address
- Sort alphabetically by last name

Create a meeting agenda template called "team-meeting-template.md".
Include:
- Date/time placeholder
- Attendees section
- 3 standing items: status updates, blockers, decisions needed
- Action items table with columns: item, owner, due date
- Notes section

The key pattern: tell Cowork the filename, the structure, and the content. It handles the formatting.

Editing Existing Files

Reading and creating are safe. Editing existing files requires a bit more care.

Safe pattern — read first, then edit:

Read "budget-2026.xlsx" and tell me what's in it.

Then, after reviewing:

In "budget-2026.xlsx", update the Q2 marketing budget from $45,000 to $52,000.
Add a new row for "AI Tools" with a budget of $3,600/year.

Why read first? Because Cowork might be looking at the wrong file, or the file might have a structure you didn’t expect. Reading first is your “measure twice, cut once” step.

Safer alternative — create new instead of editing:

Read "budget-2026.xlsx".
Create a new file called "budget-2026-updated.xlsx" with the same data,
but change the Q2 marketing budget to $52,000 and add an "AI Tools" row.
Keep the original untouched.

This gives you the updated version while preserving the original. Best of both worlds.

Organizing Files

This is Cowork’s crowd-pleaser. Everyone has messy folders. Here’s how to fix them without deleting anything important:

Organize this folder:
1. Create subfolders: Documents, Images, Spreadsheets, Archives, Misc
2. Move PDFs and DOCX files into Documents/
3. Move JPG, PNG, and GIF files into Images/
4. Move XLSX and CSV files into Spreadsheets/
5. Move ZIP and RAR files into Archives/
6. Move everything else into Misc/
7. Don't delete anything.
8. When you're done, give me a count of files in each subfolder.

Notice rule #7 — “don’t delete anything.” This is your safety net. Always include it when organizing files until you’re fully confident in how Cowork handles your stuff.

✅ Quick Check: What’s the safety rule you should include when asking Cowork to organize files?

Batch Operations

Here’s where Cowork saves the most time — repetitive work across multiple files.

Rename files based on content:

Go through every PDF in this folder.
Read the first page of each and rename the file using this format:
YYYY-MM-DD_vendor-name_amount.pdf
(extract the date, vendor, and amount from the receipt content)

Convert formats:

For each .txt file in this folder:
1. Read the content
2. Create a formatted .md version with proper headings and bullet points
3. Save the .md version in a subfolder called "formatted/"
4. Keep the originals

Extract and compile:

Read all the meeting notes in this folder (*.md files).
For each one, extract any action items (lines starting with "TODO" or "Action:").
Compile them into a single file called "all-action-items.md"
Group by person responsible, sort by date.

Ten files? Thirty files? Cowork doesn’t care. The same prompt works regardless of quantity. You just need enough context window capacity — and for very large batches, remember to break them into groups of 10-15.

The File Safety Checklist

Before any file operation, run through this mental checklist:

Am I working in the right folder? Check the file browser.
Do I have backups of anything I can’t recreate? If the file is irreplaceable, copy it somewhere else first.
Does my prompt include a “don’t delete” constraint? Always, until you’re confident.
Am I creating a new file or editing in place? Creating new is always safer.
Did I ask Cowork to read first before modifying? Review before you approve changes.

Key Takeaways

Cowork reads most common file types — txt, md, csv, xlsx, docx, pdf, json
Create new files by describing the filename, structure, and content
Read files before editing them — “measure twice, cut once”
Always add “don’t delete anything” when organizing files
Batch operations on 10-30 files are Cowork’s sweet spot
When in doubt, create a new file instead of editing the original

Up Next

You’ve got the file basics down. Next lesson, we’ll put it all together with a real project — start to finish. You’ll pick a task from your actual work and complete it entirely with Cowork.