The pdf tool appears when a table cell is clicked that contains a PDF. It can be hidden by clicking the Toggle button, as shown in the screen shot below.

Choose a probability density function from the Distribution functions drop-down list. Input fields will appear depending on the number of arguments required for the selected function.
The Upper trunc and Lower trunc fields are always available and can be used to truncate the function.
See probability density functions for a list of all PDFs.
The editor contains several tools. By using the buttons in the toolbar you can select which tool to show.
Chart The chart tool displays a graph of the current function. By using the buttons on the left hand side you can choose to plot
Delimitors and calculated values from the Calculation tool are displayed in the graph using markers.
PropertiesDisplays statistics on the currently selected function.
CalculationAllows you to calculate values and percentiles for the current function. These values are marked in the graph of the Chart tool.
InformationDescribes the currently selected function and it’s parameters.