It should have tools to mark up both text documents and graphic-heavy files like webpages.

Review and annotate: A good PDF editor should also let you or anyone else using it add comments and other annotations to PDF files during review.

A good one will perform these tasks as easily as in a text document or slide deck, allowing in-line editing, dragging-and dropping graphics, and adding or removing hyperlinks.

Content editing: Another bit of magic that PDF editors unlock is the ability to modify text insert, resize, and move images and reorganize pages in the PDF.

Likewise, a good PDF editor must be able to export PDFs into other editable formats such as Microsoft Word and PowerPoint, HTML, or plain text, maintaining the original files hyperlinks, images, and other elements. It should also include OCR technology to make the PDF text searchable and editable. A good PDF editor should be able to transform a variety of file types-from Microsoft Office formats to images to HTML-and do so seamlessly, preserving the original formatting.

Create, convert, and export PDFs: The most fundamental function of a PDF editor is to make PDFs, either from scratch, scanned hard copies, or by converting digital documents.

Call in these big dogs for anything more demanding. For these reasons, web PDF editors are best reserved for simple, fast editing jobs.

And a lot of them will watermark your edited document. With rare exception, however, they won’t let you edit existing text and many have file-size and page-volume restrictions. Generally, free online editors will let you add text and comments, merge and split documents, and convert files to and from PDF. Why spend a chunk of change on a desktop editor when free online PDF editors abound? The simple answer is because you get what you pay for.

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