A. 怎麼把網站上的pdf文件弄出來
如果是中國知網之類的學術期刊，那麼你得付費，如果只是普通的網站上的應該可以下載。如果不能下載，只可以查閱的話，我建議用截圖。然後拼裝。
B. pdf文件:下載pdf 文件打不開，刪也刪不掉
總的來說，這些PDF是個死文件，你可以將除了這些不用的文件之外的有用文件全部剪切到外面的新的文件夾，然後將死文件所在的文件夾一起刪除就可以了。你需要的PDF再重新下載。
下文是別人地方拷來的，親測有效。
My solution for this problem:
1. This kind of dead files are proced by incompletely downloading of the files from the websites.
2. When you download a pdf file from a website, rename and then save it, if the web page does not show change of the name of the pdf file, this indicates that the file have not been completely downloaded. You should immediately delete it (its size is 0 Kb.) from the folder where you save it and re-download it completely.
3. You can cut the folders in all hierarchies and files in them together or separately and paste them in other/new driver (or in new folders in new driver), since the dead files can not be moved, you can filter all dead files and re-download them according to your needs and save the in the new folders in new driver. Then you can delete the older folders in all hierarchies together with this kind of dead files completely without trouble.