It's not as easy to edit a PDF document as it is to edit most other text documents on your computer. This is because a PDF isn't really a text document; it's a snapshot of a document. It stands for Portable Document Format and is widely used across the world. If you are the original author of document, you will have no problem editing it. You'll be able to edit it in your Adobe Acrobat and won't need any other programs. If you're not the author, it'll be a little more difficult than that.
Convert your PDF document to a Microsoft Word file. You will need a PDF converter that supports Word conversions. You don't even have to download any software. Many sites will convert the document for you, and send it to you in your email. If you're don't have a specific software you prefer, try going to pdftoword.com.
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Open your new file in Microsoft Word.
Make any edits you want to the file.
Save your file once you're finished.
Go back to your PDF converter, and convert your Word document back to a PDF.
Things You'll Need
If you have Adobe Acrobat Reader, you can just open your PDF in it and edit from there. The only problem is, if your computer doesn't have the font that the PDF uses, you won't be able to edit it. Some PDF documents are locked by the original author, so you will need a password to unlock them for editing. The password will have been created by the original author of the document.