do not zip pdf file
I was surprised to receive an email with a zipped attachment which contained a pdf file. Hey, pdf file is more or less an image type and it could hardly be compressed. Further checking revealed that the original pdf file size was 4.278 MB and after zip compression, the size was 4.252 MB. The compression ratio is less than 1 %. It is just not worthwhile for both the sender and receiver wasting their time to compress and decompress the file.