Making an image darker in Acrobat is quite simple to do, as long as you know how to use the software. Adobe Acrobat is a program for creating PDFs, or Portable Document Files. Using the editing tools available only in the Adobe Acrobat Pro version, many things can be done with a document, including making an image darker. All the options to make an image darker require the use of image-editing software separate from Adobe Acrobat Pro.
Adobe Acrobat Pro is a professional, paid version of the PDF creation and editing software. The Pro version contains many editing tools. Adobe Acrobat Pro focuses mainly on the creation and conversion of text and graphical elements, like forms and tables. Although the software to darken an image is not native to Acrobat Pro, it is used by Acrobat Pro to edit images.
The process for making the images darker includes using a separate image-editing program, such as Adobe Photoshop or Illustrator. You can also use a free program, such as Photoshop Lite (also by Adobe but containing less tools and options than the original) or any program of your choosing. The image editor used must be specified as the default image-editing program for use with Acrobat Pro. Do this by opening Adobe Acrobat Pro, clicking “Edit,” “Preferences.” On the left of the window that opens, scroll down the list and click “Touchup.” When the options appear, click the "Choose Image Editor" button and select the executable file you want Acrobat to use. The executable file is the icon that opens and runs the program of choice. By default, the program used is Adobe Photoshop, if it is installed.
Use the TouchUp Object tool to select the image or object and open the image editor. To use the tool, click “Tools,” “Advanced” and then the “TouchUp Object” button. If you are editing many images, it may be easier to see the Advanced Editing Toolbar at all times. Show the toolbar by clicking “Tools,” “Advanced Editing.” At the bottom of the list, select “Show Advanced Toolbar.” With the TouchUp Object button selected, right-click on the object or image you want to edit and then click on “Edit Image” or “Edit Object,” depending what you are editing. Make the image darker according to the instructions of your editing program. In the editing program, click “File,” “Save.” This automatically saves the image in the PDF format. To access it, click on the PDF window. Do the same thing for each image or object you wish to darken or change.
Adobe Acrobat is a commercial program. To darken an image in Acrobat, you must have purchased and installed Adobe Acrobat Professional first, or you cannot use any of the editing options.