The 'Cadence Manuals.html' file is provided to allow you to review the contents before downloading the attached files; it is not for accessing the PDF files.
Therefore, you can download the attachments from the Baidu link to access the PDF files.
There may be some overlap with the PDF files included in the directory where the software is installed, but these are additionally provided on the Cadence webpage.
Many files are available that do not exist in the directory where the software is installed.