Hi,

Try the following.

1- Remove borders and outlines completely.

<img src="{{ image_data_uri(object.sudo().test_user.user_id.sign_signature) }}"

     style="width: 200px; height: auto; border: none; outline: none; box-shadow: none; background: transparent;"/>

2- Use table-borderless.

<table style="width: 100%;" class="table table-borderless">

    <tbody><tr>        

        <td style="text-align: center; vertical-align: top;" class="o_selected_td">

            <img src="{{image_data_uri(object.sudo().test_user.user_id.sign_signature)}}" style="width: 200px; height: auto;border: none !important;">

        </td>   

Hope it helps

Odoo uses an (old) external Python library to generate PDF's while your (modern) browser generates the HTML.

Browser

• highly evolved, powerful rendering engine that handle CSS, flexbox, and complex layouts with great accuracy and consistency

Python Library

• more limited rendering engine (dependent on the verion of WebKit installed ) which may not fully support all modern CSS features, especially those related to layout and borders.

Here are a few things to try:

• verify the correct version of Webkit if you are hosting Odoo yourself - https://github.com/odoo/odoo/wiki/Wkhtmltopdf
• set the "border" property to 0 or none on both the TR and TD tags
• try border: 0px; instead or border: none