After adding the pdf button, clicking the button will jump to 404

[Sheldon-Hsu]

adding the pdf button as https://timvink.github.io/mkdocs-print-site-plugin/how-to/pdf_button.html ,after the pdf button is added according to the document operation, but jump to 404 .Does anyone know how to fix this? Thanks.
my mkdocs.yml:
plugins:
- search
- print-site:
path_to_pdf: "assets/user_manual.pdf"
enumerate_headings: true
add_table_of_contents: true

pdf file is in :site/assets/user_manual.pdf

the button jump to :127.0.0.1/assets/user_manual.pdf

[stephffuller]

This looks like a case of a bad link. The /site directory is not a sub-directory of the docs directory, which is the folder that mkdocs builds from. Try moving your pdf file to somewhere inside docs, and see if that works better for you.