Maybe there's a little of misunderstanding in your question.
When you say that the files are in the same folder, I think your are talking about the
Tridion folders where components of content are located. But what you have to check is if these multimedia files have been published to the "
The problem doesn't seem to be a Tridion question, because you are talking that a certain url is not being resolved, and thus, this question is on the web server side, where Tridion publishes their pages and binary files. So the first thing to check is if the binary files (pdf) are located phisically in the path where the server is trying to reach them. If you are publishing to a certain directory in the web server side, check if the two pdf files are there.
By your question it seems that only the "file1.pdf" is going to be there. If it is so, then check that the multimedia component (pdf) in the Tridion side is used in some
Component Presentation inside a
Page, and the page is published so the binary is published with the page. Check if the binary component of "file1.pdf" is used the same way as "file2.pdf".
If all is well, then some kind of strange error is happening in the Web Server. Maybe the file names are not as you have put in the question, and some kind of strange character is making the file not accesible. Some kind of server log may be useful to discover the exact problem