Many file formats have metadata in addition to the main content. This metadata can, on a case-by-case basis, describe various additional parameters of the file's content. The title of the tab that opens the PDF is based on the metadata of the PDF file. There is a lot of information in PDF files. Most of it is used to render the document the same across different platforms. But there is also a lot of metadata: the date and time of creation and editing, which application was used, the document's subject, title, author, and much more.
This is a program with which you can edit the metadata of PDF documents. It allows you to fill in information about the author, title, subject of the document, add keywords. This program is easy to use online. This program does not require Adobe Acrobat to be installed. The program supports PDF versions of documents as well as password protected documents. In any case, if you are concerned about security, you should be careful when relying on this information because it can be edited later.