PDF Viewer Extension:

• Install the "vscode-pdf" extension from the marketplace. This extension has a built-in PDF viewer and matches your VSCode theme, so if you're using a dark theme in VSCode, the extension will display the interface elements (like toolbars) in dark mode, but it may not change the actual content of the PDF itself.

Dark Reader Extension (for full dark mode):

• For PDFs with light backgrounds, try installing the "Dark Reader" extension for VSCode. It forces a dark theme across everything in VSCode, including webview content. Sometimes, this can darken the background of PDFs too, but it may not be perfect with all files.

Alternative PDF Viewers:

• If neither option fully meets your needs, another option is using an external PDF viewer that supports dark mode, like Adobe Acrobat Reader or SumatraPDF with dark mode. They usually have advanced viewing features and make it easy to switch between light and dark backgrounds.