Many common file formats used in the AEC industry are supported. The most common are TIF, DWF and Acrobat PDF. Many other forms of PDF creation software (other than Adobe Acrobat) can produce unexpected and unpredictable results. To check how a PDF was created simply open the PDF in a text editor like WordPad. Usually in the first line it will show how it was created. If it does not say Acrobat, then it isn't an Adobe Acrobat PDF.