PDF Compatibility is key to PDF creation, which decides whether your created PDF file can be opened by Adobe Acrobat Reader software. Different versions of Adobe Acrobat Reader support differnt PDF standard. Compatibility is often stressed by publisher and publishing institutions.

PDF Standard                 Adobe Acroabt Reader
 Ver 1.2                                Version 3.x
 Ver 1.3                                Version 4.x
 Ver 1.4                                Version 5.x
 Ver 1.5                                Version 6.x
 Ver 1.6                                Version 7.x
 Ver 1.7                                Version 8.x, 9.x, and later

For example, PDF v1.4 standard PDF can be handled by Adobe Acrobat Reader 5.x and 6.x, however, there might be problems for Adobe Acrobat Reader 4.x to open and display it correctly.