How to remove bookmarks from you pdf latex file?

Option bookmarks can only be given at package loading time. Setting it later with \hypersetup will give the warning:

Package hyperref Warning: Option `bookmarks' has already been used,
(hyperref)                setting the option has no effect on input line 3.

Bookmarks can be disabled, if bookmarks=false is given to \usepackage:

\usepackage[bookmarks=false]{hyperref}

Or

\PassOptionsToPackage{bookmarks=false}{hyperref}

can be tried, before hyperref is loaded by another package or class and option bookmarks is not explicitly set by the other package or class.

If the requirements of "PDF Specification for Xplore" are holding, then you should not use hyperref at all, because links are not allowed either. Thumbnails can be added by package thumbpdf; the PDF file can be converted by pdfopt of ghostscript for fast web view.

An alternative is to use Draft mode

\usepackage{hyperref}
\hypersetup{draft}

The PDF created in Overleaf with the document class

\documentclass[conference]{IEEEtran}

passed the IEEE eXpress checking

Or just try any viewer with edition options, like the free version of PDF Exchange Viewer, with which you can remove bookmarks from any unprotected pdf file.