Compress the data in the stream using ASCII 85 encoding.
ASCII 85 replaces each five bytes of data with a four character
ASCII notation. As such it is not strictly a compression method and
it will result in the data size increasing by about twenty percent.
However the resultant data will be ASCII, which can be useful if
you need to treat the PDF data as text.
PDF streams allow a set of compression filters to be applied to
a stream of data. For example one might want to apply Flate
compression and then ASCII85 encode the result. This is represented
as two compression filters in sequence.
This function does not decompress the stream. So if compression
is already present, then this method will compress the
already-encoded data and append a compression specification to the
ABCpdf tries to avoid creating certain compression sequences.
Some compression types on some objects are illegal. Some sequences
are legal but not supported within Acrobat (though they are in most
other viewers). However these are unusual situations and you are
unlikely to ever see them.
You can override this behavior by forcing the compression to
take place. However if you do this you may end up creating a
document which is invalid or unviewable in Acrobat.