A PDF is a File Format created by Adobe that supports both Vector and Raster file types in the same document file. There are many Software Application Programs that can create a PDF File Format. Although an application can create a PDF, it may not have the needed options to screte a PDF exactly as needed.  Some of these applications are installed on your system and appear as options in 3rd party applications such as the Microsoft Office Suite to save as a PDF. Others PDF Creators are available to use online, while others require a subscription or payment such as Acrobat by Adobe. Acrobat offers powerful options, tools, and settings such as Print Output Preview, a choice of compression methods, and resolutions. Many fonts can be embedded, vectors remain editable while raster will be downsized according to the available settings. Adobe illustrator documents by default create an internal PDF within its own file format .ai that serves as the file preview and enables lower versions of illustrator and other software applications to open and edit an .ai file