diff --git a/src/js/logic/add-watermark.ts b/src/js/logic/add-watermark.ts
index 537e368..61d5a20 100644
--- a/src/js/logic/add-watermark.ts
+++ b/src/js/logic/add-watermark.ts
@@ -4,7 +4,7 @@ import {
   readFileAsArrayBuffer,
   hexToRgb,
 } from '../utils/helpers.js';
-import { state } from '../state.js';
+import { state, resetState } from '../state.js';
 
 import {
   PDFDocument as PDFLibDocument,
@@ -175,6 +175,15 @@ export async function addWatermark() {
       new Blob([newPdfBytes], { type: 'application/pdf' }),
       'watermarked.pdf'
     );
+
+    const toolid = state.activeTool;
+    resetState();
+    if (toolid) {
+      const element = document.querySelector(
+        `[data-tool-id="${toolid}"]`
+      ) as HTMLElement;
+      if (element) element.click();
+    }
   } catch (e) {
     console.error(e);
     showAlert(
diff --git a/src/tests/watermark.test.ts b/src/tests/watermark.test.ts
new file mode 100644
index 0000000..8100760
--- /dev/null
+++ b/src/tests/watermark.test.ts
@@ -0,0 +1,227 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import { state, resetState } from '../js/state';
+
+describe('Watermark Feature', () => {
+  beforeEach(() => {
+    document.body.innerHTML = `
+      <input type="text" id="watermark-text" value="Test Text" />
+      <input type="file" id="image-watermark-input" />
+      <input type="number" id="font-size" value="72" />
+      <input type="color" id="text-color" value="#000000" />
+      <input type="range" id="opacity-text" value="0.3" />
+      <input type="range" id="angle-text" value="0" />
+      <div id="text-watermark-options"></div>
+      <div id="image-watermark-options" class="hidden"></div>
+      <input type="radio" name="watermark-type" value="text" checked />
+      <input type="radio" name="watermark-type" value="image" />
+      <div id="file-display-area"></div>
+      <div id="file-controls" class="hidden"></div>
+      <button id="process-btn" disabled></button>
+      <input type="file" id="file-input" />
+      <div id="tool-content"></div>
+    `;
+
+    state.activeTool = 'add-watermark';
+    state.files = [];
+    state.pdfDoc = null;
+    state.pdfPages = [];
+    state.currentPdfUrl = null;
+  });
+
+  describe('resetState', () => {
+    it('should clear watermark text input after reset', () => {
+      const watermarkText = document.getElementById(
+        'watermark-text'
+      ) as HTMLInputElement;
+      watermarkText.value = 'CONFIDENTIAL';
+
+      resetState();
+
+      expect(state.activeTool).toBe(null);
+      expect(state.files).toEqual([]);
+      expect(state.pdfDoc).toBe(null);
+      expect(state.pdfPages).toEqual([]);
+      expect(state.currentPdfUrl).toBe(null);
+    });
+
+    it('should reset state files array', () => {
+      state.files = [new File(['content'], 'test.pdf')];
+
+      resetState();
+
+      expect(state.files).toEqual([]);
+    });
+
+    it('should reset activeTool to null', () => {
+      state.activeTool = 'add-watermark';
+
+      resetState();
+
+      expect(state.activeTool).toBe(null);
+    });
+
+    it('should reset pdfDoc to null', () => {
+      state.pdfDoc = {} as any;
+
+      resetState();
+
+      expect(state.pdfDoc).toBe(null);
+    });
+
+    it('should reset pdfPages array', () => {
+      state.pdfPages = [1, 2, 3] as any;
+
+      resetState();
+
+      expect(state.pdfPages).toEqual([]);
+    });
+
+    it('should reset currentPdfUrl to null', () => {
+      state.currentPdfUrl = 'blob:http://example.com/123';
+
+      resetState();
+
+      expect(state.currentPdfUrl).toBe(null);
+    });
+
+    it('should clear tool-content innerHTML', () => {
+      const toolContent = document.getElementById('tool-content');
+      if (toolContent) toolContent.innerHTML = '<div>Some content</div>';
+
+      resetState();
+
+      expect(toolContent?.innerHTML).toBe('');
+    });
+  });
+
+  describe('Watermark Type Toggle', () => {
+    it('should show text options by default', () => {
+      const textOptions = document.getElementById('text-watermark-options');
+      const imageOptions = document.getElementById('image-watermark-options');
+
+      expect(imageOptions?.classList.contains('hidden')).toBe(true);
+      expect(textOptions?.classList.contains('hidden')).toBe(false);
+    });
+
+    it('should have text radio checked by default', () => {
+      const textRadio = document.querySelector(
+        'input[name="watermark-type"][value="text"]'
+      ) as HTMLInputElement;
+      const imageRadio = document.querySelector(
+        'input[name="watermark-type"][value="image"]'
+      ) as HTMLInputElement;
+
+      expect(textRadio.checked).toBe(true);
+      expect(imageRadio.checked).toBe(false);
+    });
+  });
+
+  describe('Watermark Input Validation', () => {
+    it('should accept valid font size', () => {
+      const fontSize = document.getElementById('font-size') as HTMLInputElement;
+      fontSize.value = '48';
+
+      expect(parseInt(fontSize.value)).toBeGreaterThan(0);
+      expect(parseInt(fontSize.value)).toBeLessThanOrEqual(200);
+    });
+
+    it('should have default font size of 72', () => {
+      const fontSize = document.getElementById('font-size') as HTMLInputElement;
+
+      expect(parseInt(fontSize.value)).toBe(72);
+    });
+
+    it('should accept valid opacity range', () => {
+      const opacity = document.getElementById(
+        'opacity-text'
+      ) as HTMLInputElement;
+      opacity.value = '0.5';
+
+      const opacityValue = parseFloat(opacity.value);
+      expect(opacityValue).toBeGreaterThanOrEqual(0);
+      expect(opacityValue).toBeLessThanOrEqual(1);
+    });
+
+    it('should have default opacity of 0.3', () => {
+      const opacity = document.getElementById(
+        'opacity-text'
+      ) as HTMLInputElement;
+
+      expect(parseFloat(opacity.value)).toBe(0.3);
+    });
+
+    it('should accept valid angle range', () => {
+      const angle = document.getElementById('angle-text') as HTMLInputElement;
+      angle.value = '45';
+
+      const angleValue = parseInt(angle.value);
+      expect(angleValue).toBeGreaterThanOrEqual(-180);
+      expect(angleValue).toBeLessThanOrEqual(180);
+    });
+
+    it('should have default angle of 0', () => {
+      const angle = document.getElementById('angle-text') as HTMLInputElement;
+
+      expect(parseInt(angle.value)).toBe(0);
+    });
+
+    it('should accept valid hex color', () => {
+      const textColor = document.getElementById(
+        'text-color'
+      ) as HTMLInputElement;
+      textColor.value = '#FF5733';
+
+      expect(textColor.value).toMatch(/^#[0-9A-F]{6}$/i);
+    });
+
+    it('should have default color of black', () => {
+      const textColor = document.getElementById(
+        'text-color'
+      ) as HTMLInputElement;
+
+      expect(textColor.value).toBe('#000000');
+    });
+  });
+
+  describe('State Management', () => {
+    it('should maintain activeTool as add-watermark', () => {
+      expect(state.activeTool).toBe('add-watermark');
+    });
+
+    it('should start with empty files array', () => {
+      expect(state.files).toEqual([]);
+    });
+
+    it('should allow adding files to state', () => {
+      const file = new File(['content'], 'test.pdf', {
+        type: 'application/pdf',
+      });
+      state.files.push(file);
+
+      expect(state.files.length).toBe(1);
+      expect(state.files[0].name).toBe('test.pdf');
+    });
+  });
+
+  describe('UI Elements State', () => {
+    it('should have process button disabled by default', () => {
+      const processBtn = document.getElementById(
+        'process-btn'
+      ) as HTMLButtonElement;
+
+      expect(processBtn.disabled).toBe(true);
+    });
+
+    it('should have file controls hidden by default', () => {
+      const fileControls = document.getElementById('file-controls');
+
+      expect(fileControls?.classList.contains('hidden')).toBe(true);
+    });
+
+    it('should have image watermark options hidden by default', () => {
+      const imageOptions = document.getElementById('image-watermark-options');
+
+      expect(imageOptions?.classList.contains('hidden')).toBe(true);
+    });
+  });
+});