For true, high-quality scanning, or for text that is going to be reprinted, you can go up to 600 dpi. However, file sizes and download times can be prohibitive, especially when shared across the board with a vast number of documents.
Usually, the best dpi for scanning documents – balancing readability and file size – is 300 dpi. It makes the document easy to read and share.
Also, font size can affect the dpi you choose. Standard font sizes, 10-point and up, are fine at 300 dpi. However, smaller fonts might be harder to read at this resolution, so you might decide to bump it up to 400 dpi.
Also, keep in mind that with OCR you can output to a variety of file types that can affect the file size and usability of documents. These include .pdf, .jpg, .png, .tiff, and .gif formats. PDF documents are often the preferred choice because they allow you to easily convert scanned images to text that can be edited and keyword searched.
