If you are looking for a free software to edit PDF documents, you may want to check out PDF editor from Foxit software. PDF editor from Foxit Software is pretty good. Free trial edition is pretty good and trial period is six months. Free trial version puts a small watermark at the top of the document when you save the document edited.
User interface may be somewhat confusing or may be I did not explore it fully. I had to fill out few form fields in a document and the way I did was to right click on each form field and 'add text'. I had expected editing it like any word document. That was okay as long as I could edit the document without having to buy Adobe.
You can download the trial version from - http://www.foxitsoftware.com/pdf/pe_intro.php.
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