I recently found my self scouring the web to find out how to check the dpi (dots per inch) of a PDF I had created. I figured it would be quite simple, but there was not much help out there, so I leaned on my AIGA listserv to see if they could help. They came through with flying colors. Here is a guide to checking the dpi of a pdf.
First off I am using Adobe Acrobat Professional 8.1.6 running on Mac OS X 10.4.11 and have created the pdf with InDesign C3. This wont work if you are just using Adobe Reader.
Open the .pdf file you are looking to check out in Adobe Acrobat Professional.
Once the file is open, click “preflight…” under the “Advanced” menu drop down [Advanced–>preflight...]
This should open up a dialogue box like the one below.
Click the triangle next to the PDF analysis category to reveal all its options.
Scroll down and click on the “List images below 250 ppi”. As a side note, ppi (points per inch) is the same as dpi.
*Some versions might not have all the tasks categorized, so just scroll and find “List images below 250 ppi”.
As you will notice, for my purposes 250 ppi will not work (I need 800), so we will have to edit it. So click on the Edit button in the window’s menu bar while you have “List images below 250 ppi” selected. If 250 ppi works for you, skip to Step 6.
*Please note that Adobe Acrobat Professional version 8.1.6 does not give me the option to duplicate the task and then edit. I just edited this one because it will serve the same purpose of finding images below 250 when I execute it.
Under the Edit Profile, you will need to change the Name and the Purpose to correspond with your needs. Since I wanted to make sure my pdf was 800 dpi, I need to edit the task so that it checks for images under 801 dpi. If I make it 800 dpi and it happens to be 800 dpi, then this task will run clean thereby not telling me the dpi of my pdf.
Next, click on the “Images” category under the “List images below 801 ppi” (the name has been automatically updated once I edited it in the previous step) and change 250 to 801 in the dialogue box “lower than” under the “Resolution of color and grayscale images is”. Click OK.
Now you need to execute the task by clicking “Execute” while the “List images below 801 ppi” is selected. You should have automatically been taken back to the “Profiles” tab once you clicked OK in the last step.
When the task is executing you should get a box that looks like this:
Once the file has finished executing, the “Results” tab should appear and if your pdf was below 801 dpi (or your desired dpi) a registry will appear that looks like this:
Click the expanding arrow next to the first “Information Dot” to reveal your desired information. According to this summary, my file was not the desired 800 dpi, rather it was 300 dpi. Now I know I need to go back into InDesign and re-export my file with different settings to make my file 800 dpi. Then I can recheck it using steps 1, 2, 6 and 7. You wont need to edit the task again because it will already be saved.
I hope this guide will be usefull to some of you. It’s a pretty basic operation, you just might not know where the appropriate tools are to perform it. Heck, I didn’t.