Encode a number into a PDF string. This format may be needed for
direct insertion into a content stream.
PDF content streams accept certain formats of numbers. In many
situations these are the same as the strings returned by .NET
functions such as ToString. However in the case of floating point
conversions, not all output formats are valid in a PDF content
For example, very small or very large numbers can lead to the
insertion of exponential format strings which are not an accepted
PDF format and can lead to errors. Because numbers typically occur
in a non exponential range these errors can be infrequent and
difficult to track down.
This method will produce PDF valid strings for use in content
streams and similar applications.