PDFs should be one of the most straightforward document types in the world, but unfortunately they are not so simple when it comes to editing them. Paid-for PDF editors can do it all, but do you really want to pay for a tool to complete a quick and easy editing job? As we have learned from this round-up of free tools and services, you may not need to.

Adobe invented the PDF (Portable Document Format) to solve a problem that dogged people for years: how to view and print documents without requiring the original software that document was created in or the fonts it uses. It wasn't meant to be a replacement for a word processor - it was a layout format for precise alignment of text and images.

Many programs can save documents in PDF format, but few can edit them directly. But what if you receive a document in PDF form and need to change it? Or you might save a file as a PDF but lose the original (editable) document through a disk or human error? In all of these situations, you need a PDF editor.

However, here's the thing: free PDF editors generally do not allow you to edit text. What they offer is the ability to erase (or 'whiteout') text and replace it with new text. Matching the font, both size and colour, but it's all you'll be able to do if you can't get hold of the original file used to create the PDF.

Some free PDF editors let you annotate PDFs and add or remove pages. The original content cannot be changed, but you can insert notes and comments, use a highlighter pen, strikethrough text, delete pages, fill out forms and so on.

Here are some of your options:

AbleWord

AbleWord

AbleWord is the only free PDF editor we're aware of that can import a PDF and make it completely editable. It's best when importing PDF files that were created in Word, but will attempt to replicate all PDF files. The end result won't look identical to the original but will be close.

Foxit Reader

Foxit Reader

Foxit Reader is a lightweight alternative to Adobe Reader and many people prefer it. It's more than just a PDF reader though and it has a wide range of powerful tools. You cannot edit the contents, but text can be struck through with a line and replaced by a pop-up note.

PDF-Xchange Viewer

PDF-Xchange Viewer

PDF-XChange Viewer offers an almost identical set of features to Foxit Reader and it is useful for annotating in a similar manner.

PDF Candy

PDF Candy

As long as your editing demands aren't too heavy, PDF Candy may be the quickest solution. It can convert PDFs to other formats, rotate them, split them, protect them and add watermarks.

This new online service has but one limitation: any file you upload must be under 10MB. But that's it: there are no ads or any other restrictions.

LibreOffice

LibreOffice

LibreOffice, the free Office alternative, is worth considering if you want to edit the text in a PDF file. It loads PDFs and it can cope with very large documents with hundreds of pages. The only snag is that each line of text is text box, which makes it awkward to edit large amounts of text.

PDF Pro

PDF Pro

PDF Pro is an online tool that lets you upload three PDF files per month and edit them. The latest update includes a facility to convert PDF documents to Word (.doc) format, which not many free products can do.

FormSwift PDF Editor

FormSwift PDF Editor

FormSwift is another online PDF editor. You simply drag and drop files to upload them, and you can then edit them in your browser before downloading and printing or sharing.

You can edit text by deleting and replacing it, add images or signatures. It's relatively basic, but it's free and requires only an internet connection.

PDF to Word

PDF to Word

PDF to Word does exactly what the name says. You select a file on your PC, upload it to the site and it emails you the Word document a minute or two later. The advantage of this is that you can use Word or another word processor to edit the text and resave the document as a PDF.