pdf檔的問題

this is depends on the pdf file is how to create ....
sometimes when the creater create the pdf from word file, they have keep the fonts and transfer the data/formatting to the pdf...so the Words on the pdf document can be select and copy....

but sometimes...when the file is Print to a pdf ....than the words on the pdf should be read as a image .....and not able to select and copy to other application ....