When using a PDF file in Visio, it will initially be one grouped object. the best format to use is WMF. When opening the Windows Metafile, it should be come into Visio as one grouped object. In order to explode all of the individual, editable objects, you must right click on it and choose “Group, Ungroup” to unlock the contents. This may take a while if your file contains a very detailed drawing. In some cases, Visio will hit a practical limit and may stop responding. This is likely if the drawing has more then 200,000 objects. Stick with it, and it will eventually finish digesting the file. You’ll be presented with a drawing where every object is separate and highlighted in pink. In order to edit one object, you need to deselect everything by clicking somewhere outside the boundaries of the drawing and then select just the object you want to edit. It’s a good idea to immediately delete any sections of the drawing that you do not need as speed will improve as the number of object calculations decreases.