Update docx, xlsx, pdf, pptx skills with latest improvements (#330)

docx: Add commenting and track-changes support. Reorganize OOXML
tooling into a shared office/ module.

pptx: Streamline SKILL.md, add slide-editing and pptxgenjs guides,
bundle html2pptx as a tgz. Reorganize OOXML tooling into a shared
office/ module.

xlsx: Move recalc script into scripts/ and expand it. Add shared
office/ module for OOXML pack/unpack/validate.

pdf: Improve form-filling workflow with new form-structure extraction
script and updated field-info extraction.

skills/pdf/SKILL.md

@@ -1,6 +1,6 @@
 ---
 name: pdf
-description: Comprehensive PDF manipulation toolkit for extracting text and tables, creating new PDFs, merging/splitting documents, and handling forms. When Claude needs to fill in a PDF form or programmatically process, generate, or analyze PDF documents at scale.
+description: Use this skill whenever the user wants to do anything with PDF files. This includes reading or extracting text/tables from PDFs, combining or merging multiple PDFs into one, splitting PDFs apart, rotating pages, adding watermarks, creating new PDFs, filling PDF forms, encrypting/decrypting PDFs, extracting images, and OCR on scanned PDFs to make them searchable. If the user mentions a .pdf file or asks to produce one, use this skill.
 license: Proprietary. LICENSE.txt has complete terms
 ---
 
@@ -8,7 +8,7 @@ license: Proprietary. LICENSE.txt has complete terms
 
 ## Overview
 
-This guide covers essential PDF processing operations using Python libraries and command-line tools. For advanced features, JavaScript libraries, and detailed examples, see reference.md. If you need to fill out a PDF form, read forms.md and follow its instructions.
+This guide covers essential PDF processing operations using Python libraries and command-line tools. For advanced features, JavaScript libraries, and detailed examples, see REFERENCE.md. If you need to fill out a PDF form, read FORMS.md and follow its instructions.
 
 ## Quick Start
 
@@ -166,6 +166,26 @@ story.append(Paragraph("Content for page 2", styles['Normal']))
 doc.build(story)
 ```
 
+#### Subscripts and Superscripts
+
+**IMPORTANT**: Never use Unicode subscript/superscript characters (₀₁₂₃₄₅₆₇₈₉, ⁰¹²³⁴⁵⁶⁷⁸⁹) in ReportLab PDFs. The built-in fonts do not include these glyphs, causing them to render as solid black boxes.
+
+Instead, use ReportLab's XML markup tags in Paragraph objects:
+```python
+from reportlab.platypus import Paragraph
+from reportlab.lib.styles import getSampleStyleSheet
+
+styles = getSampleStyleSheet()
+
+# Subscripts: use <sub> tag
+chemical = Paragraph("H<sub>2</sub>O", styles['Normal'])
+
+# Superscripts: use <super> tag
+squared = Paragraph("x<super>2</super> + y<super>2</super>", styles['Normal'])
+```
+
+For canvas-drawn text (not Paragraph objects), manually adjust font the size and position rather than using Unicode subscripts/superscripts.
+
 ## Command-Line Tools
 
 ### pdftotext (poppler-utils)
@@ -284,11 +304,11 @@ with open("encrypted.pdf", "wb") as output:
 | Create PDFs | reportlab | Canvas or Platypus |
 | Command line merge | qpdf | `qpdf --empty --pages ...` |
 | OCR scanned PDFs | pytesseract | Convert to image first |
-| Fill PDF forms | pdf-lib or pypdf (see forms.md) | See forms.md |
+| Fill PDF forms | pdf-lib or pypdf (see FORMS.md) | See FORMS.md |
 
 ## Next Steps
 
-- For advanced pypdfium2 usage, see reference.md
-- For JavaScript libraries (pdf-lib), see reference.md
-- If you need to fill out a PDF form, follow the instructions in forms.md
-- For troubleshooting guides, see reference.md
+- For advanced pypdfium2 usage, see REFERENCE.md
+- For JavaScript libraries (pdf-lib), see REFERENCE.md
+- If you need to fill out a PDF form, follow the instructions in FORMS.md
+- For troubleshooting guides, see REFERENCE.md