PDF is a popular and widely supported document format. It was developed in 1993 in its very first version. When checking a PDF document (and some other files that can contain PDF information), you can find information about the PDF Version of the document.
The PDF version released in 1993 is known as version 1.0 . Since then, many version updates followed. Version 1 ranged from version 1.0 to 1.7 but is now outdated. The PDF format was treated with a major update to version 2.0 in 2017.
Checking your document for the PDF Version can come pretty in handy though. The format is very flexible and, of course, e.g. PDF 1.2 documents can be opened in the newest Adobe PDF Reader. In some cases, newer PDF versions can be opened and viewed in older readers as well. They might omit or not correctly displayed items and elements that rely on the updated versions though. By checking the PDF Version, you can check whether your document might cause trouble because the version is not entirely supported by your PDF reader.