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Built-in Skills: Documents, Spreadsheets, Presentations

Earlier in this chapter, you learned how to create custom Skills—encoded expertise that teaches Claude specific procedures. But Cowork also comes with built-in Skills for common document formats. These are pre-installed capabilities that work out of the box.

What Built-in Skills Are​

Built-in Skills are domain-specific capabilities Anthropic has developed and optimized:

SkillFile TypesWhat It Does
docx.docxRead, create, and edit Word documents
xlsx.xlsxRead, analyze, and modify spreadsheets
pptx.pptxCreate and edit PowerPoint presentations
pdf.pdfExtract text and structure from PDFs

These Skills are pre-installed—you don't need to create or configure them. They're automatically available when working with these file types in Cowork.

The docx Skill: Word Documents​

Capabilities:

  • Create new Word documents with proper formatting
  • Edit existing documents while preserving structure
  • Work with tracked changes
  • Maintain styles, headers, footers, and page layouts
  • Add tables, lists, and formatting

Example prompt:

"Create a Word document called 'meeting-notes.docx' with:

  • Title: 'Q1 Planning Meeting - January 15, 2026'
  • Attendees section with placeholder names
  • Agenda items: Budget Review, Timeline Discussion, Resource Allocation
  • Action items table with columns: Task, Owner, Due Date
  • Professional formatting with headers and bullet points"

What Claude does:

  1. Creates the .docx file
  2. Adds formatted content with proper document structure
  3. Applies styles for headings, lists, and tables
  4. Produces a file you can open directly in Word

Advanced operations:

"Open 'proposal-draft.docx', find all instances of 'Q1 2026' and replace with 'Q2 2026'. Add a tracked changes comment explaining the update. Preserve all existing formatting."

Tracked changes support: When editing existing documents, Claude can use Word's tracked changes feature so you can review modifications before accepting them.

Limitations:

  • Complex layouts (newsletters, brochures) may not preserve perfectly
  • Macros and VBA are not executed or modified
  • Very large documents (>100 pages) may have processing delays

The xlsx Skill: Spreadsheets​

Capabilities:

  • Read spreadsheet data intelligently
  • Analyze data and generate insights
  • Add or modify rows and columns
  • Create formulas that reference existing data
  • Generate charts and visualizations
  • Preserve formatting and existing formulas

Example prompt:

"Read 'sales-data.xlsx'. Analyze the sales figures and:

  • Calculate total sales by region
  • Identify top 5 products by revenue
  • Find month-over-month growth rate
  • Add a new tab called 'Summary' with this analysis in a clean table
  • Create a bar chart showing sales by region"

What Claude does:

  1. Reads the spreadsheet data
  2. Analyzes patterns and calculates metrics
  3. Creates a new worksheet with the summary
  4. Generates a chart based on the data
  5. Updates the file while preserving original data

Formula awareness: Claude understands spreadsheet formulas and can:

  • Explain what existing formulas do
  • Create new formulas using appropriate functions
  • Reference cells correctly when adding data
  • Avoid breaking formula dependencies

Best practices:

  • Always back up spreadsheets before bulk modifications
  • Test formula changes on a small sample first
  • Ask Claude to explain formulas you don't understand

Limitations:

  • Very complex spreadsheets with thousands of formulas may be slow
  • Custom functions and add-ins are not executed
  • Power Query and Power Pivot operations may not preserve perfectly

The pptx Skill: Presentations​

Capabilities:

  • Create presentation decks from outlines
  • Add and arrange slides
  • Format text, shapes, and images
  • Apply consistent themes
  • Add speaker notes

Example prompt:

"Create a PowerPoint presentation called 'product-update.pptx' with:

  • Title slide: 'Q1 Product Roadmap Update'
  • Overview slide with key achievements
  • 3 feature spotlight slides with bullet points
  • Timeline slide showing Q2 plans
  • Conclusion slide with next steps
  • Use a professional design with consistent colors throughout"

What Claude does:

  1. Creates the presentation file
  2. Adds slides with proper layouts
  3. Formats content consistently
  4. Applies a theme with unified styling
  5. Includes speaker notes for key points

Working with existing presentations:

"Open 'deck-template.pptx'. Update the data slide with new figures from 'q1-results.xlsx'. Add two slides at the end summarizing key takeaways. Match the existing design style."

Limitations:

  • Complex animations and transitions may not preserve
  • Embedded videos and media may need manual re-linking
  • Highly custom slide layouts may not replicate perfectly

The pdf Skill: PDF Content​

Capabilities:

  • Extract text content from PDFs
  • Identify document structure (headings, sections)
  • Understand tables and data in PDFs
  • Work with both text-based and scanned PDFs (OCR)

Example prompt:

"Read 'contract-2024.pdf'. Extract and summarize:

  • Key terms and obligations
  • Payment schedule and amounts
  • Important dates and deadlines
  • Any unusual or concerning clauses Organize this into a structured summary document."

What Claude does:

  1. Extracts text from the PDF
  2. Identifies document structure and sections
  3. Organizes key information logically
  4. Creates a readable summary with proper formatting

PDF limitations:

  • Images within PDFs are described, not analyzed visually
  • Highly formatted layouts may lose some structure
  • Password-protected PDFs cannot be read
  • Some PDFs with complex formatting may have extraction errors

When to Use Built-in vs. Custom Skills​

Use built-in Skills when:

  • Working with standard document formats
  • You need format preservation
  • The task involves reading/writing Office documents
  • You want reliable, tested functionality

Use custom Skills when:

  • You have domain-specific procedures
  • You need consistent reasoning patterns
  • Built-in capabilities don't cover your use case
  • You want to encode expertise that applies across document types

Example combination:

  • Built-in docx Skill for Word document creation
  • Custom Skill for "legal contract review" reasoning
  • Combined: Claude creates a properly formatted document AND applies legal analysis expertise

Capability Matrix​

Taskdocxxlsxpptxpdf
Read content✓✓✓✓
Create new✓✓✓✗
Edit existing✓✓✓✗
Format preservation✓✓✓N/A
FormulasN/A✓N/AN/A
Charts/visualsLimited✓LimitedN/A
Tracked changes✓N/AN/AN/A

Best Practices​

For documents (docx):

  • Use tracked changes when editing important documents
  • Describe the desired structure clearly
  • Specify formatting requirements explicitly

For spreadsheets (xlsx):

  • Always back up before bulk operations
  • Ask Claude to explain formulas before applying them
  • Test on a small sample when modifying large datasets

For presentations (pptx):

  • Provide an outline for better structure
  • Specify design requirements (colors, fonts, themes)
  • Review generated slides for consistency

For PDFs:

  • Understand that extraction may have errors
  • Verify important information against the original
  • Use PDFs as reference, not as editable source

Try With AI​

**🔍 Explore Built-in Skills:"

"Choose a document format I work with regularly (Word, Excel, PowerPoint, or PDF). Create a simple example file and ask Claude to do something useful with it using the built-in Skill. What works well? What are the limitations?"

What you're learning: Hands-on capability assessment—understanding what built-in Skills can actually do by testing them. Direct experience is more valuable than reading documentation.

**💡 Combine Built-in and Custom:"

"Design a workflow that uses both a built-in Skill and a custom Skill. For example: Use the docx Skill to create a document, combined with a custom Skill for domain-specific content generation (like 'technical documentation' or 'marketing copy')."

What you're learning: Skill composition—understanding how to combine built-in capabilities with custom expertise. This combination is where Cowork becomes most powerful.

**🏗️ Test Real-World Scenarios:"

"Pick a real document I've worked with recently. How could Claude's built-in Skills have helped? Recreate a simplified version and test. What would have saved me time?"

What you're learning: Practical application—connecting Cowork's capabilities to your actual work. Identifying real opportunities to apply these Skills makes the learning concrete.

What's Next​

You've explored Cowork's interface, workflows, browser integration, connectors, and built-in Skills. The final lesson in this Cowork section brings everything together with a decision framework—helping you choose between Claude Code and Claude Cowork for any given task, and understanding when to use both together.