If you are making money online by creating and selling eBooks online, you definitely need software which can create, edit and modify PDF file. When it comes to PDF files, the first thing which comes to mind is Adobe Acrobat. But if you are thinking of creating eBooks without spending any money, Adobe Acrobat is not the software for you because you need to pay for the copy. The best alternative free software that works just like Microsoft Office and Adobe Acrobat that you can find online will be Apache Open Office. This software is free to download and it works well with PDF file.
But if you are on the road without your laptop and you desperately require software to edit a small mistake on your eBook, you probably need something online or browser base software which you can edit or modified PDF file. If you are able to find a computer which has internet access, try PDFescape. Registration is not necessary but the PDF files uploaded will not be saved. PDF files uploaded will be deleted once the browser is closed. It should be fine it you are using it for emergency purposes and temporally. But there will be some restriction as the file upload must be less than 10 MB and less than 100 pages. And of cause you can only perform simple edit or modification.