You can not upload a PDF to timeline on Android, but can send it to somebody via Messenger in Messenger Lite, or share it to a Group. Find out how to post a PDF file to a Facebook group.
Step 1: Open FB app on your Android phone, then tap hamburger icon at the top-right corner;
Step 2: Scroll the screen and choose Groups, select the group you need to post PDF to;
Step 3：Hit Files, click plus icon to upload a PDF to the group. Once the PDF uploaded, you have posted the PDF.