diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 89f1eaa..4cdb729 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -125,8 +125,8 @@ jobs:
           # Verify combined PDF
           test -f _site/docs.pdf || (echo "Missing docs.pdf" && exit 1)
 
-          # Verify single preview image for combined PDF
-          test -f _site/preview.png || (echo "Missing preview.png" && exit 1)
+          # Verify single preview image for combined PDF (derived from PDF name)
+          test -f _site/docs.png || (echo "Missing docs.png" && exit 1)
 
           # Verify .md links were rewritten to .html
           if grep -q '\.md"' _site/docs/index.html; then
@@ -319,20 +319,20 @@ jobs:
             body += `**Single-file mode (test-output-single):**\n`;
             body += `- resume.pdf\n`;
             body += `- index.html\n`;
-            body += `- preview.png\n\n`;
+            body += `- resume.png\n\n`;
             body += `**Combined mode (test-output-combined):**\n`;
             body += `- docs.pdf (combined)\n`;
             body += `- index.html (auto-generated index)\n`;
             body += `- docs/*.html (individual pages)\n`;
-            body += `- preview.png\n\n`;
+            body += `- docs.png\n\n`;
             body += `**Collection mode - flat (test-output-collection-flat):**\n`;
             body += `- resume.pdf, cover-letter.pdf, references.pdf\n`;
             body += `- resume.html, cover-letter.html, references.html\n`;
-            body += `- *-preview.png (one per document)\n\n`;
+            body += `- *.png (one per document)\n\n`;
             body += `**Collection mode - nested (test-output-collection-nested):**\n`;
             body += `- projects/web/*.pdf, projects/mobile/*.pdf\n`;
             body += `- projects/web/*.html, projects/mobile/*.html\n`;
-            body += `- *-preview.png (one per document)\n`;
+            body += `- *.png (one per document)\n`;
             
             await github.rest.issues.createComment({
               owner: context.repo.owner,
diff --git a/action.yml b/action.yml
index 90c679c..c4c4f96 100644
--- a/action.yml
+++ b/action.yml
@@ -23,9 +23,9 @@ inputs:
     required: false
     default: 'index.html'
   output-preview:
-    description: 'Output preview image filename (without extension)'
+    description: 'Output preview image filename (without extension). Defaults to PDF name if not set.'
     required: false
-    default: 'preview'
+    default: ''
   preview-dpi:
     description: 'Preview image resolution in DPI'
     required: false
@@ -166,7 +166,13 @@ runs:
           BASE_URL="https://${{ github.repository_owner }}.github.io/${{ github.event.repository.name }}"
         fi
 
-        PREVIEW_URL="${BASE_URL}/${{ inputs.output-preview }}.png"
+        PDF_NAME="${{ inputs.output-pdf }}"
+        PREVIEW_NAME="${{ inputs.output-preview }}"
+        if [ -z "$PREVIEW_NAME" ]; then
+          PREVIEW_NAME="${PDF_NAME%.pdf}"
+        fi
+
+        PREVIEW_URL="${BASE_URL}/${PREVIEW_NAME}.png"
         PAGE_URL="${BASE_URL}/"
 
         cat > /tmp/og-header.html << 'HEADER_EOF'
@@ -182,8 +188,8 @@ runs:
           --include-in-header=/tmp/og-header.html \
           --lua-filter="${{ github.action_path }}/filters/mdlinks-to-html.lua"
 
-    - name: Generate HTML pages (multi-file mode)
-      if: ${{ inputs.sources != '' }}
+    - name: Generate HTML pages (multi-file combined mode)
+      if: ${{ inputs.sources != '' && inputs.mode == 'combined' }}
       shell: bash
       run: |
         set -euo pipefail
@@ -195,7 +201,13 @@ runs:
           BASE_URL="https://${{ github.repository_owner }}.github.io/${{ github.event.repository.name }}"
         fi
 
-        PREVIEW_URL="${BASE_URL}/${{ inputs.output-preview }}.png"
+        PDF_NAME="${{ inputs.output-pdf }}"
+        PREVIEW_NAME="${{ inputs.output-preview }}"
+        if [ -z "$PREVIEW_NAME" ]; then
+          PREVIEW_NAME="${PDF_NAME%.pdf}"
+        fi
+
+        PREVIEW_URL="${BASE_URL}/${PREVIEW_NAME}.png"
         PAGE_URL="${BASE_URL}/"
 
         cat > /tmp/og-header.html << 'HEADER_EOF'
@@ -218,6 +230,40 @@ runs:
             --lua-filter="${{ github.action_path }}/filters/mdlinks-to-html.lua"
         done < /tmp/mdpress_files.txt
 
+    - name: Generate HTML pages (multi-file collection mode)
+      if: ${{ inputs.sources != '' && inputs.mode == 'collection' }}
+      shell: bash
+      run: |
+        set -euo pipefail
+
+        REPO_NAME="${{ github.event.repository.name }}"
+        if [ "${{ github.repository_owner }}" = "${{ github.event.repository.name }}" ]; then
+          BASE_URL="https://${{ github.repository_owner }}.github.io"
+        else
+          BASE_URL="https://${{ github.repository_owner }}.github.io/${{ github.event.repository.name }}"
+        fi
+
+        while IFS= read -r SRC; do
+          REL="${SRC#./}"
+          DEST="_site/${REL%.md}.html"
+          PREVIEW_URL="${BASE_URL}/${REL%.md}.png"
+          PAGE_URL="${BASE_URL}/${REL%.md}.html"
+          mkdir -p "$(dirname "$DEST")"
+
+          cat > /tmp/og-header.html << HEADER_EOF
+        <meta property="og:type" content="website">
+        <meta property="og:image" content="${PREVIEW_URL}">
+        <meta property="og:url" content="${PAGE_URL}">
+        <meta name="twitter:card" content="summary_large_image">
+        <meta name="twitter:image" content="${PREVIEW_URL}">
+        HEADER_EOF
+
+          echo "Converting $SRC -> $DEST"
+          pandoc -s "$SRC" -o "$DEST" \
+            --include-in-header=/tmp/og-header.html \
+            --lua-filter="${{ github.action_path }}/filters/mdlinks-to-html.lua"
+        done < /tmp/mdpress_files.txt
+
     - name: Generate index page (multi-file mode, combined)
       if: ${{ inputs.sources != '' && inputs.mode == 'combined' }}
       shell: bash
@@ -284,7 +330,13 @@ runs:
     - name: Generate preview image (single-file or combined mode)
       if: ${{ inputs.sources == '' || inputs.mode == 'combined' }}
       shell: bash
-      run: pdftoppm "_site/${{ inputs.output-pdf }}" "_site/${{ inputs.output-preview }}" -png -singlefile -rx ${{ inputs.preview-dpi }} -ry ${{ inputs.preview-dpi }}
+      run: |
+        PDF_NAME="${{ inputs.output-pdf }}"
+        PREVIEW_NAME="${{ inputs.output-preview }}"
+        if [ -z "$PREVIEW_NAME" ]; then
+          PREVIEW_NAME="${PDF_NAME%.pdf}"
+        fi
+        pdftoppm "_site/$PDF_NAME" "_site/$PREVIEW_NAME" -png -singlefile -rx ${{ inputs.preview-dpi }} -ry ${{ inputs.preview-dpi }}
 
     - name: Generate preview images (collection mode)
       if: ${{ inputs.sources != '' && inputs.mode == 'collection' }}
diff --git a/docs/configuration.md b/docs/configuration.md
index c9864df..5817dfe 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -8,7 +8,7 @@
 | `sources` | Space or newline separated list of Markdown files or glob patterns (multi-file mode) | — |
 | `output-pdf` | Output PDF filename | `document.pdf` |
 | `output-html` | Output HTML filename | `index.html` |
-| `output-preview` | Output preview image filename (without extension) | `preview` |
+| `output-preview` | Output preview image filename (without extension) | PDF name |
 | `preview-dpi` | Preview image resolution in DPI | `150` |
 | `mode` | Multi-file mode: `combined` (single PDF) or `collection` (separate PDFs) | `combined` |
 | `index-title` | Title for auto-generated index page (multi-file mode) | `Index` |