When saving scanned file as PDF, its too large

Updated: 05/16/2020 by Computer Hope
Adobe PDF file icon.

Below are the most common causes for a scanned document to be too big in size when saved as a PDF (Portable Document Format) file. Most users notice the PDF is too large when they try sending the PDF in e-mail and realize it exceeds the allowable size. Most e-mail services don't allow attached files larger than 3 to 5 MB.


The DPI (dots per inch) of the scanned image is often the primary cause of a large PDF file. By default, most scanners record images at 300 DPI, which is the minimum DPI for any image that is printed after scanned. However, for a PDF that is for screen reading, the DPI should be 72.

Saving as color

Because most scanned objects are text-only documents, they do not need to be in color. Make sure the images are black and white and not color.

Color settings

Even after setting your scanner to black and white some scanner software may keep other color settings enabled. After setting the image to black and white, make sure any color settings, such as "Color Depth," are also decreased.

PDF convert

If you tried the suggestions above, and the image size is small, but the PDF is still large, it may be the conversion software's fault. Make sure the settings in the software that converts the PDF are properly set. Again, we suggest making sure the PDF resolution is 72 DPI. PDF programs may also have different ways to save a PDF. For example, in PrimoPDF, you can save the PDF as "Screen," "eBook," "Print," and "Prepress." For most users the PDF file needs to be viewed on the screen, so the "Screen" setting could be used.

Adobe Acrobat Pro

If you have the non-free version of Adobe Acrobat Pro, this program can also shrink the PDF using the Reduced in size option under Document. Alternatively, you can use the PDF Optimizer in Advanced.

Other e-mail suggestions

If you've tried the suggestions above and the file size is still too big for e-mail, consider the suggestions below.