To change the background color of a PDF to white, you need to use a PDF editor. Here are the steps to follow to change the background color of a PDF to white using Adobe Acrobat:
Open the PDF in Adobe Acrobat.
Go to "Tools" in the top menu and select "Fill & Sign".
Click the "Add Background" button.
In the "Add Background" dialog box, select "White" as the color and click "OK".
Save the changes to the PDF by going to "File" and selecting "Save As".