To change the font style in a PDF signature in Odoo, you need to follow these steps:

1. Go to the "Settings" menu in Odoo and select "Users & Companies" option.
2. Select the user whose signature you want to change and click on the "Edit" button.
3. Scroll down to the "Signature" section and click on the "Edit" button next to the signature field.
4. In the signature editor, select the text that you want to change the font style of.
5. Click on the "Font" dropdown menu in the toolbar and select the font style that you want to use.
6. The text will now be displayed in the new font style. Click on the "Save" button to save your changes.

Note: The font styles available in the dropdown menu may vary depending on the PDF editor you are using in Odoo.

Hi,

Since you mentioned signing the PDF I hope you are familiar with sign module. In the PDF, you'll have the place to sign. When you click on that a pop up opens where you'll be able to write the full name and choose or draw a signature. Under the Auto tab, you'll have the option to generate signature and there will be a style option where you can choose the font styles of the signature.

Regards