The contents in my pages are showing twice, and I don't know why. In admin section, the content of every page is type once, but is published twice.

www.psolpr.org.br

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It probably was a temporary problem with the database, the site is already loading, and the problem remains. All pages show contents twice.

I've changed the layout of frontpage/postpage, and I did it changing index.php. But I can't find the .php file for the pages.

well, if you changed index.php and you have a problem, I'd have to guess that the change is causing the problem. there is probably a bug in your change, you need to review it. To see if that is the problem, rename your changed inxed.php to index_changed.pgp and upload a fresh copy. if the posts are correct, then it's your changes that are causing the problem.