I cannot make a good title for this problem..
When I read pdf file usually I can see some line.
I think it is not hardware problem because sometimes it disappear.
Is this normal?

It's only on PDF files, harpum?

If it's showing up for everything, I'd say it was a screen defect, but if it's only on PDFs ... well I'm not sure what to think of that.... http://www.dbstalk.com/images/smiles2/kopfkratz.gif

I cannot make a good title for this problem..
When I read pdf file usually I can see some line.
I think it is not hardware problem because sometimes it disappear.
Is this normal?
You are not alone, I have seen these line in the same area on screen, too.
I think, it happens sometimes [but seldom] on my iLiad when I flip pages in short interval. After the next flip they are gone again. This should be a pdf viewer bug.

"good title" mmh, reading the headline I thougt you have a problem with dust etc. on screen. :rolleyes5

[EDIT] I found my one old horizontal line in pdf file (http://www.mobileread.com/forums/showthread.php?t=7196&highlight=horizontal+line) thread. This occurs when the pdf viewer doesn't like the "splitting in several parts" in image stream of pdf file.

I realize this line is exact same to boundary which you can get after rotation. So I think this pdf viewer also prepare rotation and it make a problem.

Does this happen on all your pdf files? Or not?
Is problem pdf file a scanned document [images embedded in pdf] or pure text?
Uploading your problem pdf could help, to check out, whether it is visible on other iLiads too.
I realize this line is exact same to boundary which you can get after rotation. So I think this pdf viewer also prepare rotation and it make a problem.
-> no hardware bug at specific location on screen. This could be the same problem as in the other thread [link above].

:happy2: I thought you meant litterally, 'Clean the screen'.
It's one of these tiny things with readers that are annoying. In a paper book every time you turn a page, it's new and clean. With a reader it accumulates specks of every type, finger smuges, spittle and whatnots. I keep a lint free rag for cleaning glasses in the box next to it.

One software cutie for the reader would be to have an optional cover page of the book you're reading in permanent display.