In order to change styles in the PDF, like the image width, title color and similar elements, you need to write inline styles in the item elements. Some experience of HTML is required.
You can create a template override of the default_item.php file and rename it to pdf_item.php.
In that file, you can edit the img element in line 52 and write style="width: 50px" to set a custom image width.
You can also change the a element in line 62 (or wrap the text of line 64 in a <p> element) and add style="color: #f00; font-size: 25px" to make it larger and red.
Let me know if that helps.
