I was contacted and asked to write about PDF Compressor. It is a freeware and at v.3.0.
As its name suggests it is straightforward with one purpose. It is easy to use, simply add or drag and drop pdf files to the program window or alternatively add a folder containing pdf files. Customize the output folder and if necessary the output defaults from 120 dots per inch and 75% compression. Press the Start button and it is done.
In tests on an older XP computer the process took 3 minutes for a 39MB file and approximately 20 seconds for a 4MB one. The most important thing to look for is of course the size of the output. As the author states:
First please check if your PDF files are scanned PDF or not. Scanned PDF documents are made from images so that the program can compress it. If the PDF files are not scanned PDF, the compressor will not work properly and make files bigger than before.
The usefulness of PDF Compressor, and this is true of other similar software too, is therefore limited. The size reduction does depend on the original pdf, if the original is a manual or book it is likely not going to be compressed. Changing the DPI and compression quality will help but may adversely effect text quality in the file.