XLSX is a more modern version of the spreadsheet format, a type of e-book within the Microsoft Office Excel suite. It takes its name from the Microsoft Excel Open XML Document. This format has replaced the XLS. Initially included in the paid package of MS Office, but then the Open XML standard was recognized as public. As in XLS, the data is placed in the cells of the table, however, it uses data compression like ZIP. This reduces file size and increases the potential for data security. Data can be entered into the cells manually, as well as by automatic calculations - when special formulas are entered into the cells, starting with the equal sign.
PDF is short for Portable Document Format, which can be translated from English as “Portable Document Format”. It was developed by Adobe Systems for use by US federal authorities as a tool for storing working documents. This is a universal cross-platform format, which is now standard for electronic documents. It serves to convert text files (including photographs or other images) into electronic documents without any loss. To read PDF files you need special programs - Adobe (Acrobat) Reader, PDF-Viewer and others.