Optimize Content Streams
This option removes redundant content streams and shared portions of content streams found in a PDF document.
Compress all Uncompressed Streams
The CompressStreams option finds content streams in a PDF document that are not compressed and then compresses them using the Flate method.
Recompress LZW Compressed Streams Using Flate
You can use this option to replace the compression method used with images in a PDF document, from LZW to Flate. This method appears in some old PDF documents but it is rarely used any longer. Flate is much more widely used than LZW, and it tends to compress better, so it is generally better to replace LZW with Flate.
Note that Recompression only works with images, while ReplaceLZW applies to all streams in a PDF document.
Compress Document Body
All releases of the PDF specification after PDF 1.6 have been able to apply compression to a PDF document as a whole, rather than merely compress individual content streams within a document. This generally leads to a much smaller document. That is how the CompressDocumentStructure option works.
Any document handler built to the specifications of PDF 1.6 or later should be able to open and view these compressed documents.
Discard ASCII Filters
PDF permits two filters, ASCIIHex and ASCII85, to encode binary data into an ASCII only format. These were originally used both to allow a document to pass through a 7 bit data path without losing information and as an aid in debugging PDF documents with binary data. Both of these formats increase the size of a stream considerably. They can be removed and will not change the document appearance. The one area where removing these filters could cause a problem is for PDF documents that must pass through a path that is not safe for 8 bit binary data, but this generally no longer applies.
The linearization process for a PDF document places all of the information needed to render the first page of the document near the start of the file. This allows a web browser to open the PDF document more quickly. The first page renders promptly and subsequent pages are rendered in the background. Using the PDF alternate file format for linearized documents is well suited for displaying PDF documents on the web, but it tends to result in a slightly larger file.