Whether other users occur this issue? Please check whether your PDF file and the document library have unique permission.
Open the details pane > Manage access > Advanced, you could check your user permission.
And you could try to share the PDF file with user.
For Reference:
https://learn.microsoft.com/en-us/sharepoint/troubleshoot/administration/access-denied-or-need-permission-error-sharepoint-online-or-onedrive-for-business
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