Sign PDF – Frequently Asked Questions

The Sign PDF tool is a free online service that allows you to add electronic signatures to your PDF documents quickly and easily.

Key Features:

• Draw Signatures: Draw your signature with mouse or touch using Fabric.js canvas
• Upload Signatures: Upload signature images (PNG, JPG) from scanned or photographed signatures
• Multi-Page Support: Sign multiple pages in one PDF
• Signature Modal: Preview and create signatures in a dedicated modal window
• Session Storage: Reuse signatures across multiple pages without redrawing
• Resize & Move: Adjust signature placement, size, and rotation after placing

Technical Implementation: The tool uses Fabric.js for the signature drawing canvas and object manipulation. When you draw a signature, it's rendered on a Fabric.js canvas in a modal window. The signature is then saved to session storage as a base64 data URL, allowing reuse across multiple pages. When placing signatures, they become Fabric.js image objects that can be moved, resized, and rotated. Server-side, FPDI and TCPDF embed the signatures as images on the PDF pages.

Drawing a signature is simple with the signature drawing modal.

How to Draw Your Signature:

1. Upload PDF: Upload the PDF document you want to sign
2. Click "Draw Signature": A modal window opens with a blank drawing canvas
3. Draw: Use your mouse (desktop) or finger (mobile/tablet) to draw your signature
   • The canvas uses Fabric.js for smooth, responsive drawing
   • Draw naturally as you would on paper
4. Preview: See your signature in real-time as you draw
5. Clear (if needed): Click "Clear" button to erase and redraw
6. Save Signature: Click "Save Signature" when satisfied
7. Close Modal: The modal closes and your signature is stored in session storage
8. Place Signature: Click anywhere on the PDF to place your signature

Drawing Features:

• Smooth Lines: Fabric.js provides smooth, natural-looking pen strokes
• Touch Support: Works with finger drawing on touchscreens
• Canvas Size: Adequate canvas size for comfortable signature drawing
• Black Ink: Signatures are drawn in black for professional appearance

Yes! You can upload an existing signature image instead of drawing one.

How to Upload a Signature Image:

1. Click the "Upload Signature" button
2. Select an image file from your device:
   • PNG (recommended for transparent backgrounds)
   • JPG/JPEG
   • Other common image formats
3. The image is loaded and stored in session storage as base64
4. Click anywhere on the PDF to place the uploaded signature

Sources for Signature Images:

• Scanned Signature: Scan your handwritten signature on paper
• Photographed Signature: Take a photo of your signature on white paper
• Previously Created: Use a signature image you've saved before
• Digital Signature: Create a signature in graphic design software

Best Practices for Signature Images:

• White Background: Sign on white paper for easy background removal
• High Contrast: Use dark pen/ink for clear visibility
• PNG with Transparency: Remove background for professional appearance
• Good Resolution: Higher resolution images scale better
• Cropped: Crop tightly around signature to remove excess white space

Absolutely! The Sign PDF tool supports multi-page signing.

How to Sign Multiple Pages:

1. Create Signature: Draw or upload your signature once
2. Sign First Page: Click on the first page to place your signature
3. Navigate to Next Page: Use page navigation buttons (Previous/Next)
4. Sign Additional Pages: Click to place signature on other pages
   • Your signature is stored in session storage, so you don't need to redraw/re-upload
5. Repeat: Navigate to all pages that need signing and place signatures
6. Save PDF: All signatures from all pages are included in the final PDF

Multi-Page Signing Features:

• Signature Reuse: Create signature once, use on all pages
• Independent Placement: Each page stores its signature placements separately
• Different Positions: Place signature in different locations on different pages
• Multiple Signatures Per Page: Add multiple signature instances to the same page

Common Use Cases:

• Contracts: Sign every page of multi-page contracts
• Forms: Sign multiple signature fields in long forms
• Acknowledgments: Sign each page to acknowledge review
• Legal Documents: Initial every page and sign final page

The signature modal provides a dedicated space for creating and previewing signatures before placement.

Modal Features:

For Drawn Signatures

• Drawing Canvas: Fabric.js canvas for smooth signature drawing
• Live Preview: See your strokes in real-time as you draw
• Clear Button: Erase and start over if not satisfied
• Save Button: Store signature when finished

For Uploaded Signatures

• Image Preview: See uploaded signature image
• File Selector: Choose image from device
• Automatic Storage: Image stored in session after upload

Why Use a Modal?

• Focused Environment: Dedicated space for signature creation without PDF distraction
• Better Preview: Larger canvas for easier drawing
• Quality Control: Verify signature looks good before placing on PDF
• User Experience: Clear workflow (create → preview → save → place)

Modal Workflow:

1. Click "Draw Signature" or "Upload Signature"
2. Modal opens with canvas or file selector
3. Create/upload signature
4. Preview signature in modal
5. Click "Save Signature" to store in session
6. Modal closes, return to PDF
7. Click on PDF to place signature

Session storage is browser-based temporary storage that allows signature reuse during your current session.

What Is Session Storage?

• Type: Browser-based storage (similar to cookies but temporary)
• Lifespan: Lasts only for the current browser tab/session
• Scope: Specific to the current tab (not shared across tabs)
• Cleared: Automatically cleared when you close the browser tab

How Signatures Are Stored:

• Drawn Signatures:
  • Fabric.js canvas is converted to a data URL (base64-encoded PNG image)
  • Data URL stored in session storage with key like 'userSignature'
  • Format: data:image/png;base64,iVBORw0KG...
• Uploaded Signatures:
  • Image file converted to base64 data URL
  • Stored in session storage using same key

Benefits of Session Storage:

• Signature Reuse: Draw/upload once, use on multiple pages
• No Re-uploading: Navigate between pages without losing signature
• Automatic Cleanup: Signature data automatically cleared when tab closes
• Privacy: Signature only exists in your browser, not sent to server until final save

Session Storage vs. Local Storage:

• Session Storage: Cleared when tab closes (more secure for signatures)
• Local Storage: Persists even after browser closes (not used for signatures for privacy)

Yes! Signatures are fully editable after placement with complete manipulation controls.

Signature Manipulation:

Moving Signatures

• Click and Drag: Click on signature to select it, then drag to new position
• Fine Positioning: Move signature precisely to align with signature lines or fields

Resizing Signatures

• Corner Handles: Click signature to show selection handles in corners
• Drag Handles: Drag corner handles to resize larger or smaller
• Proportional Scaling: Hold Shift (desktop) to maintain aspect ratio
• Custom Size: Make signature larger for prominent placement or smaller for initials

Rotating Signatures

• Rotation Handle: Some Fabric.js configurations show rotation handle above signature
• Drag to Rotate: Rotate signature to match document angle or preference

Deleting Signatures

• Select and Delete: Click signature, press Delete or Backspace key
• Replace: Delete and place new signature if positioning is wrong

Technical Details:

• Signatures are Fabric.js Image objects with full manipulation capabilities
• Transform controls enabled for move, resize, rotate
• Selection handles provide visual feedback

Yes! The Sign PDF tool is fully optimized for mobile devices with touch support.

Mobile Features:

• Touch Drawing: Draw signatures naturally with your finger on touchscreens
• Photo Upload: Upload signature images from device camera or photo library
• Tap to Place: Tap anywhere on PDF to place signature
• Touch Manipulation: Pinch to resize, drag to move signatures
• Responsive Modal: Signature modal optimized for mobile screen sizes
• Page Navigation: Swipe or tap to navigate between pages

Mobile Tips:

• Use landscape orientation for larger drawing canvas
• Draw slowly for smoother signature lines on touchscreens
• Use stylus (if available) for more precise signature drawing
• For uploaded signatures, photograph your signature on white paper for best results

Device Support:

• iOS (iPhone, iPad) - Safari, Chrome
• Android (phones, tablets) - Chrome, Firefox
• All modern touchscreen devices

No, we do not permanently store signatures or documents.

How We Handle Your Data:

• Signatures (Client-Side):
  • Stored in your browser's session storage only
  • Never sent to server until you click "Save PDF"
  • Automatically cleared when browser tab closes
  • Only exists in your browser's memory
• PDF Files (Server-Side):
  • Original PDF temporarily stored in /tmp folder during processing
  • Signed PDF created with embedded signatures
  • All temporary files deleted after download
  • Not stored permanently on server

Privacy Guarantee:

• We do not save or analyze your signatures
• We do not have access to your signature data (stored client-side)
• We do not permanently store your signed PDFs
• All processing is temporary and session-isolated

Security Measures:

• HTTPS encryption for all uploads and downloads
• Client-side signature storage (more secure)
• Automatic file cleanup after session

The output is a standard PDF file with signatures embedded as images.

Output File Details:

• Filename: signed_[timestamp].pdf
  • Example: signed_20250116_162045.pdf
• PDF Version: PDF 1.7 or higher
• Signatures: Embedded as PNG or JPEG images on PDF pages
• Compatibility: Opens in all PDF readers
  • Adobe Acrobat Reader
  • Web browsers
  • Mobile PDF apps

Signature Embedding:

• Signatures are placed as image layers on top of PDF pages
• Images are positioned at exact coordinates where you clicked
• Base64 signature data is decoded and embedded permanently
• Final PDF cannot be edited without PDF editing software

The Sign PDF tool uses cutting-edge web technologies for signature creation and placement.

Frontend Technologies:

• Fabric.js: Interactive canvas library
  • Signature drawing canvas in modal
  • Signature image objects with manipulation (move, resize, rotate)
  • Smooth drawing with touch and mouse support
• Session Storage API: Browser storage for signature reuse
  • sessionStorage.setItem('signature', dataURL)
  • sessionStorage.getItem('signature')
• Canvas API: For signature rendering
  • canvas.toDataURL() – Convert drawn signature to base64 image
• Modal UI: Dedicated signature creation interface
• JavaScript (ES6+): Signature management and UI interactions
• PDF.js: Renders PDF pages for visual placement

Backend Technologies:

• FPDI: Imports original PDF pages
• TCPDF: Embeds signature images on pages
  • Image() method for placing signatures
  • Base64 image decoding
• PHP 7.4+: Server-side processing and coordinate conversion

Processing Workflow:

1. User creates signature (draw or upload) in modal
2. Signature converted to base64 data URL
3. Signature stored in session storage
4. User clicks on PDF pages to place signatures
5. All signature placements (positions, pages) tracked by JavaScript
6. On "Save PDF," signature data and positions sent to server
7. FPDI imports pages, TCPDF embeds signatures at specified positions
8. Signed PDF generated and downloaded