docs: add development roadmap for next features

- Prioritized list of 6 features to implement next
- Sprint planning with time estimates
- Clear rationale for implementation order
- Expected outcomes and API coverage improvements

This roadmap provides a clear path for the next 3 weeks of development.

Author: jdrhyne

DEVELOPMENT_ROADMAP.md

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+# Development Roadmap - Nutrient DWS Python Client
+
+## 📊 Issue Review & Recommendations
+
+After reviewing all open issues and analyzing the codebase, here are my recommendations for what to tackle next:
+
+### 🥇 **Top Priority: Quick Wins (1-2 days each)**
+
+#### 1. **Issue #11: Image Watermark Support** ⭐⭐⭐⭐⭐
+- **Why**: 80% already implemented! Just needs file upload support
+- **Current**: Supports `image_url` parameter
+- **Add**: `image_file` parameter for local image files
+- **Effort**: Very Low - mostly parameter handling
+- **Value**: High - common user request
+
+#### 2. **Issue #10: Multi-Language OCR Support** ⭐⭐⭐⭐
+- **Why**: Small change with big impact
+- **Current**: Single language string
+- **Add**: Accept `List[str]` for multiple languages
+- **Effort**: Low - update parameter handling and validation
+- **Value**: High - enables multi-lingual document processing
+
+### 🥈 **Second Priority: Core Features (3-5 days each)**
+
+#### 3. **Issue #13: Create Redactions Method** ⭐⭐⭐⭐
+- **Why**: Complements existing `apply_redactions()`
+- **Value**: Complete redaction workflow
+- **Complexity**: Medium - new API patterns for search strategies
+- **Use cases**: Compliance, privacy, legal docs
+
+#### 4. **Issue #12: Selective Annotation Flattening** ⭐⭐⭐
+- **Why**: Enhancement to existing `flatten_annotations()`
+- **Add**: `annotation_ids` parameter
+- **Effort**: Low-Medium
+- **Value**: More control over flattening
+
+### 🥉 **Third Priority: High-Value Features (1 week each)**
+
+#### 5. **Issue #16: Convert to PDF/A** ⭐⭐⭐⭐
+- **Why**: Critical for archival/compliance
+- **Value**: Legal requirement for many organizations
+- **Complexity**: Medium - new output format handling
+
+#### 6. **Issue #17: Convert PDF to Images** ⭐⭐⭐⭐
+- **Why**: Very common use case
+- **Value**: Thumbnails, previews, web display
+- **Complexity**: Medium - handle multiple output files
+
+### 📋 **Issues to Defer**
+
+- **Issue #20: AI-Powered Redaction** - Requires AI endpoint investigation
+- **Issue #21: Digital Signatures** - Complex, needs certificate handling
+- **Issue #22: Batch Processing** - Client-side enhancement, do after core features
+- **Issue #19: Office Formats** - Lower priority, complex format handling
+
+### 🎯 **Recommended Implementation Order**
+
+**Sprint 1 (Week 1):**
+1. Image Watermark Support (1 day)
+2. Multi-Language OCR (1 day)
+3. Selective Annotation Flattening (2 days)
+
+**Sprint 2 (Week 2):**
+4. Create Redactions Method (4 days)
+
+**Sprint 3 (Week 3):**
+5. Convert to PDF/A (3 days)
+6. Convert PDF to Images (3 days)
+
+### 💡 **Why This Order?**
+
+1. **Quick Wins First**: Build momentum with easy enhancements
+2. **Complete Workflows**: Redaction creation completes the redaction workflow
+3. **High User Value**: PDF/A and image conversion are frequently requested
+4. **Incremental Complexity**: Start simple, build up to more complex features
+5. **API Coverage**: These 6 features would increase API coverage significantly
+
+### 📈 **Expected Outcomes**
+
+After implementing these 6 features:
+- **Methods**: 18 total (up from 12)
+- **API Coverage**: ~50% (up from ~30%)
+- **User Satisfaction**: Address most common feature requests
+- **Time**: ~3 weeks of development
+
+## 🚀 Current Status
+
+As of the last update:
+- **PR #7 (Direct API Methods)**: ✅ Merged - Added 5 new methods
+- **PR #23 (OpenAPI Compliance)**: ✅ Merged - Added comprehensive documentation
+- **Current Methods**: 12 Direct API methods
+- **Test Coverage**: 94%
+- **Python Support**: 3.8 - 3.12
+
+## 📝 Notes
+
+- All features should maintain backward compatibility
+- Each feature should include comprehensive tests
+- Documentation should reference OpenAPI spec where applicable
+- Integration tests should be added for each new method