If you\u2019ve never used Gimp\u2014a free\u00a0image editor available for GNU\/Linux, OS X, Windows and other operating systems\u2014you might be quite surprised by its capabilities\nI use it for everything from Facebook posts when the available backgrounds don\u2019t work well for what I want to say to political buttons that I design and press out using a button-making machine.\n\nGimp can do everything from resizing and cropping images to adding text, changing colors or distorting images in artistic ways. You can use it to draw with its pencil or paintbrush and layer additional images. It\u2019s quite a versatile tool. Yet I only recently noticed that it can also be used to manipulate PDF files, not just the many types of image files that most people use it to create, modify or enhance.\nWhy Gimp?\nIt might not be obvious why you\u2019d want to modify PDFs using Gimp, but it can do some interesting things. Even though PDFs normally contain a lot of text and maybe some images, there are a number of ways that you can work with them using Gimp. For example, you can:\n\nTurn a PDF into a series of image files (one per page)\nDelete specific pages\nAdd some new pages\nWhite out or replace select portions of pages\nAdd notes or images\nReverse the order of the pages\nBreak a PDF into separate PDFs\u2014by chapter, for example\n\nIt\u2019s important to understand that editing PDFs using Gimp means you are modifying page images, and this is something that you need to fully grasp before you get started.\nIn addition, you need to know a few tricks about how Gimp works before you try using it to manipulate PDFs.\nOpening your PDF\nOnce you\u2019re ready to try using Gimp to make changes to a PDF, here\u2019s how to start:\nFirst, open Gimp.\nNext, when you go to open a PDF using Gimp, you need to decide whether to open its pages as separate images or as a group of layers, which are portions of a single image.\nThis choice makes a big difference. If you plan to export the modified document as a PDF, you need to open it with the \u201cOpen pages as layers\u201d option, which is the default. Once the document is open, you should see each page displayed as a layer in Gimp\u2019s layers panel. If you don\u2019t, try selecting Windows -> Dockable Dialogs -> Layers and it should appear. Don\u2019t be surprised when a 100-page PDF ends up with 100 layers. That\u2019s the way it works.\nSelect your file (e.g., Win_at_Sudoku.pdf) by selecting Open\u2026 under the File menu, selecting the PDF you want to open and then clicking on Import at the bottom right. Alternately, you can go directly to the File -> Open as layers\u2026 option and choose the PDF file.\nIn the panel that opens, you can change the page size and select the page range or just go with the defaults, which select all pages using 700x925 pixels. Then click on \u201cImport\u201d at the bottom right.\nIn the Layers panel, you will then see a list of the layers with small images of each one and \u201ceye\u201d icons on the left of each layer that controls whether the layers are visible, though the active (first) page will be the one that is displayed.\nMaking changes\nTo work on a single page, click on the image of that layer from the layers panel to make it the active layer and click on (sometimes referred to as \u201cunclicking\u201d) the eye icons for the other images so that they are no longer\u00a0visible. You will then be able to draw on the selected page or add text to it. If you add text, you will be creating a new layer, but you can to use the \u201cMerge visible layers\u201d option to turn the two or more layers back into a single layer when you are ready. Since the other layers should not be visible at that time, they will not be affected.\nAlso note that if you don\u2019t merge layers of text that you add they will end up as separate pages when you export your modified PDF.\nRemoving pages\nYou can remove pages in any of three ways. You can make them invisible before you save the new PDF; you can select multiple pages (and no others) and use the \u201cmerge visible pages\u201d options to reduce them to only the first page in the list; you can simply click on them and select \u201cdelete layer\u201d.\nAdding pages\nYou can add pages to your document by adding layers and sliding them into the proper position in the document by clicking on them and then using the up and down tools shown at the bottom of the layers panel to move them into the correct location.\nYou can add text and images to new layers. Just remember to have no other pages visible when you merge the added layers and the associated text layers.\nSaving your changes\nWhen you are ready to export the modified file, make sure that all of the layers you want to retain are visible (eye icons displayed) and select File -> Export As\u2026 using .pdf as the file extension for your new document. As explained earlier, if you want to omit any pages, make sure they are not visible by clicking on (\u201cunclicking\u201d) the eye icon. Make sure you export with \u201clayers as pages\u201d so you don\u2019t end up with a single page (all pages merged into one). Select these options for the export:\n\nLayers as pages\nReverse the pages order\nApply layer masks before saving\nOmit hidden layers and layers with zero opacity\n\nYour \u201cLayers as pages\u201d option may also say \u201cbottom layers first\u201d. If so, this will change to \u201ctop layers first\u201d once you click on the \u201cReverse the pages order\u201d option.\nTurning a PDF into a group of images\nIf you open a PDF as separate images rather than layers, you can save each page as an independent PDF or as a separate image. Gimp will create the files using whatever file extension you select. So, just use the appropriate file extension and Gimp will do what\u2019s needed. You will, however, have to save each page separately.\nWrap-Up\nGimp can be handy for making a number of changes to PDF files, but because it works with images, it\u2019s not the best tool for inserting or modifying a lot of text. For that, you\u2019re much better off using a PDF editor. Please keep in mind that you should get used to this process before using it on important files or, better yet, always keep a copy of the original file so that you can start over again if you make a mistake.