Download a pocket folder template online and save it on your desktop. Do a "Save As," and rename it so you still have the original file should you need it once you have made changes. This can be found by typing "free design template" on a Google search. Open InDesign, create a new document, and open your template by clicking "File," then "Open," then "Desktop," and then double-click your downloaded file.
Delete any text or images that may be on your free template. Customize the size on the template you have downloaded by selecting the outer edge of the folder outline. Once you select the outer edge of the folder, look at the x and y dimensions at the top of the toolbar and adjust to the dimensions you want. Do the same for the flaps of the folder at the bottom of the page.The template shows exactly where the folds will be, so be sure to think about how tall or short you want the inside flaps of the folder to be.
Place text or graphics on your folder. On the template, the right side of the folder is the front of the folder, the left side is the back, and the flaps at the bottom of the page will be folded up once printed. (Therefore any text on the flaps will need to be written upside down.)
Test print your folder to ensure that everything is how you want it. Fold everything where it should be folded to ensure that you did not type any text upside down. Once you are satisfied with the design, either save the file as a PDF and send it to a printer, or purchase heavy duty paper (cardstock or thicker) and print your custom pocket folder.