Endnote does not recognize relevant information of a pdf file

My endnote cannot discover relevant document information when I import a downloaded pdf file into my library:

For some pdf files, endnote can discover all relevant information about the document and import them into library properly – authors’ list, article title, journal title, DOI etc.; for many other pdf files, it cannot discover these information and the fields in the imported articles are blank. I do find DOI information show up in the “summary” window in the imported files, so document related information should be imbedded in the pdf file.

I wonder if there is anything I can do to increase the chance for endnote to automatically discover document related information from downloaded pdf files.

By the way: I am using Endnote 20; operating system windows 10; Internet browser is microsoft edge.

Thank you very much for any help!