I have made some tests and successfully renamed more than one file using your copy/paste technique so I don't think the problem has to do with the number of files renamed in the same session. Problems appear when the copy includes characters that can not be used in files names ('\', '/', ':', '"', '*', '<', '>', '|',/n...). This can happen, as example, if you select the invisible line break character at end of line, or select more that one line, when copying the text from the document. Because the paste operation is not checking this (I have now fixed it) these invalid characters remain in the edit box and when we click enter, the rename fail.
Even so this is not the best way to rename files with PDF Explorer. The best technique is to use the QuickInfoEdit mode (F4). In this mode the text copied can be easily redirected to the metadata fields using the QuickPaste assistant that popup after all text copy operations.
Tip: After all the metadata fields are edited for one document pass to the previous/next one using the keyboard shortcuts CTRL+Up/CTRL+Down.
When all the documents you want to rename have the metadata fields edited you only need to use the Rename batch tool (first in the list of the available batch tools). With this batch tool you can compose the new file name using the metadata fields contents so with the same copy/paste tedious tasks (improved by the QuickPaste assistant) you get the metadata info fields filled and file renamed.
File names with meaningful names are good but if metadata fields are properly filled you just need to use the DBSearch scan mode to easily find the document you want to consult, much more easy than using the shell to discover the right file name.
