The Share Content option only shares entire screens, windows, PowerPoint files, and whiteboards. This is by design. To share a .pdf or word files, you need to share your desktop and then open the files for participants to view.
In addition, for the ability to share files directly, you can also propose it in Team User Voice. I found similar feedback that you can vote for. Many features of our current products are designed and upgraded based on customers’ feedback. With requirements like this increase, the problem may well be released in the future. Thanks for your understanding and support.
Feedback: Share a custom file
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.