add: create Acrobat usage guide with steps for signing PDFs and include relevant images

Author: tigran-sargsyan-w

docs/Acrobat_Usage_Guide.md

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+# How to Sign PDFs Using Adobe Acrobat and a Self-Signed Certificate
+
+This guide explains how to use your self-signed `.p12` digital certificate, created with the `create_certificate.sh` script, to sign PDF documents using **Adobe Acrobat Reader** or **Acrobat Pro**.
+
+---
+
+## 🪪 Steps to Add a Certificate-Based Signature to a PDF
+
+### 1. Open the Certificate Tool
+
+- Open a PDF in **Adobe Acrobat**.
+- Go to:    
+```All Tools → More → Use a Certificate```
+- **Alternatively:**  
+  From the Acrobat Home screen:    
+  ```See All Tools → Protect → Use a Certificate → Select your PDF file```
+
+
+### 2. Open the "Use a Certificate" Panel
+
+- The **Use a Certificate** panel will appear on the left.
+- Choose one of the following options:
+
+| Option                        | Description                                      |
+|------------------------------|--------------------------------------------------|
+| **Certify (visible signatures)**   | Creates a visible digital signature field       |
+| **Certify (invisible signatures)** | Certifies the document without visible signature |
+
+- Then click:
+  ```Drag New Signature Rectangle```
+
+![Use a Certificate panel](../docs/images/acrobat_certify_visible.png)
+
+### 3. Confirm Certification
+
+- Click **OK** in the **Save as Certified Document** dialog box.
+
+
+### 4. Define Signature Placement (Visible Only)
+
+- If you selected **Certify (visible signatures)** in step 2:  
+  Use your mouse to **drag a rectangle** where the signature should appear on the page.
+
+
+### 5. Choose a Digital ID
+
+- In the **Sign with a Digital ID** dialog:
+  - Select an existing digital ID (e.g. your `.p12` certificate).
+  - Or click:
+    ```Configure New Digital ID```
+    to import or create a new one.
+
+![Digital ID selection screenshot](../docs/images/acrobat_digital_id_dialog.png)
+
+
+### 6. Review and Sign
+
+- Click **Review** to inspect the document content before signing.
+- Click **Sign**.
+- Save the document when prompted.
+
+✅ Your PDF is now **digitally certified**.
+
+---
+
+## 🧾 Certifying and Signing Documents
+
+The **Use a Certificate** tool in Adobe Acrobat provides two types of certificate-based signatures:
+
+| Option          | Description                                                                 |
+|-----------------|-----------------------------------------------------------------------------|
+| **Digitally Sign** | Adds an **approval signature**, indicating that the signer approves the content |
+| **Certify**        | Provides a **higher level of control** — certifies the document's integrity and defines allowed changes |
+
+
+### 🔐 Certify (Visible or Invisible Signatures)
+
+- Certification **must be done before any other signatures** are added.
+- Once a document is signed, certification options become unavailable.
+- When certifying a document, you can control whether:
+  - Changes are allowed (form fill-ins, comments, none, etc.)
+  - A visible signature is shown or not.
+
+
+### ✅ Compliance Standards
+
+Both **Certify** and **Digitally Sign** options are compliant with:
+
+- **ETSI** (European Telecommunications Standards Institute)
+- **PAdES** (PDF Advanced Electronic Signature)
+
+> Acrobat and Reader support multiple PAdES parts depending on configuration:
+>
+> - **Part 2:** Default PDF signing format
+> - **Part 3:** CAdES format (optional, can be enabled)
+> - **Part 4:** Long-term validation (LTV) and timestamping (supported since Acrobat 9.1)
+
+You can customize the **default signing method or format**:
+
+```Edit → Preferences → Signatures → Creation & Appearance → More...```
+
+---
+
+## ⚙️ Setting Up Certificate-Based Signatures
+
+To improve the signing experience and prevent errors:
+
+### ✅ Preparation Steps
+
+- 📥 **Obtain a digital ID**:  
+  Get it from your organization, a trusted provider, or create a **self-signed certificate** (see: `create_certificate.sh`).
+  
+- ⚙️ **Set the default signing method** in Acrobat Preferences.
+  
+- 🎨 **Create a visual signature appearance**  
+  (see section: *Create the Signature Appearance*)
+
+- 🛑 **Use Preview Document mode**  
+  Prevents hidden dynamic content from misleading you into signing something you can't see.  
+  
+- 📄 **Review all pages**  
+  Signature fields can exist on multiple pages — don’t miss any.
+
+- 🧩 **Configure the application**  
+  Both the **author and signer** should set up Adobe’s signature environment properly  
+  (see: *Set Signing Preferences* below).
+
+- 📝 **Choose the signature type**  
+  Understand the difference between **approval** and **certification** signatures.
+
+📎 *Note: Some organizations require digital IDs issued only by internal authorities.*
+
+---
+
+## 🛠️ Set Signing Preferences
+
+Signing preferences define what happens when the signature dialog opens. These control:
+
+- Which actions are allowed or restricted
+- Visibility of signature field data
+- How document content can influence the signature process
+
+🧭 Go to:
+```Edit → Preferences → Signatures → Creation & Appearance → More...```
+
+For enterprise-level control and configuration, refer to:  
+**Adobe Digital Signatures Guide** (PDF link available on Adobe's site)
+
+---
+
+## 🖊️ Create the Appearance of a Certificate-Based Signature
+
+You can customize the **visual look** of your certificate-based signature in Acrobat’s **Signature Preferences**. This allows you to include:
+
+- An image of your handwritten signature
+- A company logo
+- A photo or stamp
+- Additional signer information (reason, contact, etc.)
+
+You can also create **multiple signature styles** for different purposes.
+
+
+![Signature formats example](../docs/images/acrobat_signature_formats.png)
+
+
+### ✨ How to Create a Custom Appearance
+
+1. *(Optional)* Scan your **handwritten signature** and save it as an image (e.g. PNG or JPG).
+2. Open the PDF and **right-click** on the signature field →  
+   ```Select `Sign Document` or `Certify with Visible Signature` ```
+3. In the Sign dialog box, find the **Appearance** drop-down menu and select:
+   ```Create New Appearance```
+4. In the **Configure Signature Appearance** dialog:
+   - Type a **short, descriptive name** for this appearance (e.g. "Tigran Handwritten Logo").
+
+### 🖼️ Configure Graphic
+
+Choose how the graphic appears in the signature box:
+
+| Option           | Description                                                                 |
+|------------------|------------------------------------------------------------------------------|
+| **No Graphic**   | Displays only text fields and the default icon                              |
+| **Imported Graphic** | Shows your custom image (handwritten signature, logo, etc.)                 |
+| **Name**         | Displays only the icon and your name (from the certificate)                 |
+
+If using **Imported Graphic**:
+- Select `File` → `Browse` → choose your image file
+
+
+### 📝 Configure Text
+
+You can choose which text fields will appear:
+
+- **Name, Organization, Country** (from your `.p12` / certificate)
+- **Reason for signing**
+- **Location**
+- **Contact information**
+
+These fields can help **verify the authenticity** and purpose of the signature.
+
+
+### 🧩 Text Properties
+
+In the same dialog box, you can also:
+
+- Set **text direction** (LTR or RTL)
+- Choose **digit format**
+- Adjust layout
+
+If the dialog includes **Additional Signature Information**, fill in:
+
+- Reason
+- Location
+- Contact info
+
+> These options are only available if previously enabled in:
+>
+> ```Preferences → Signatures → Creation & Appearance → More...```
+
+
+### 📎 Access Preferences Anytime
+
+You can also create or edit signature appearances via the menu:
+
+- On **Windows**:
+  ```Hamburger menu (☰) → Preferences → Signatures```
+- On **macOS**:
+  ```Acrobat → Preferences → Signatures```
+
+Then go to:
+```Creation & Appearance → More...```
+
+---
+
+## 🔐 PKCS#12 Modules and Tokens
+
+You can manage **multiple digital IDs** for different signing roles or purposes — for example:
+
+- Signing as an individual
+- Signing on behalf of a company
+- Using different methods (e.g. visible vs invisible certification)
+
+Digital IDs are typically **password-protected** and can be stored in various locations:
+
+| Storage Type            | Description                                           |
+|-------------------------|-------------------------------------------------------|
+| **PKCS#12 file (.p12)** | Local file on your computer (default for this toolkit) |
+| **Smart card / token**  | External hardware (e.g. USB-based identity devices)   |
+| **Windows certificate store** | System-level certificate manager (Windows only)     |
+| **Roaming ID**          | Hosted on a server — used in enterprise environments  |
+
+🛠 Adobe Acrobat includes a **default signature handler** that supports IDs from all of the above.
+
+📌 To use a certificate, make sure it's **registered** and visible inside Acrobat (via Preferences → Signatures → Identities).
+
+---
+
+## 🕒 Add a Timestamp to Certificate-Based Signatures
+
+You can include a **timestamp** in your certificate-based signature, showing **exactly when** the document was signed. Timestamps help:
+
+- Prove when the signature was created
+- Reduce risk of invalidation due to expired certificates
+- Assist in long-term validation
+
+### 🕹 Where the Timestamp Comes From:
+
+| Source                    | Behavior                                                                 |
+|---------------------------|--------------------------------------------------------------------------|
+| **Trusted Timestamp Authority (TSA)** | Preferred — secure and verifiable via a third-party certificate        |
+| **Local system time**     | Used if no TSA is configured — may be unreliable for legal verification |
+
+🖊️ The timestamp appears:
+- In the **signature field** itself
+- In the **Signature Properties** dialog, under the **Date/Time** tab
+
+---
+
+### 📝 Notes:
+
+- You can configure Acrobat to use a TSA (Preferences → Signatures → Timestamping).
+- If no timestamp server is set, Acrobat will use your computer’s local time.
+- **Missed it?** You can **add a timestamp later** to a signature  
+  → See: *Establish long-term signature validation*
+