With MobiPDF, you can replace an image inside any PDF from the "Edit" tab. Here is how.
1. Open your MobiPDF file.
2. Click the Edit tab and select Images.
3. Select the image you want to replace. In the Properties panel, click Replace Picture.
4. In the File Explorer, select the image you want to insert and click Open.
5. Use the dragging points and Properties options to adjust your image.