The Web-client does not have a formal upper limit on document file sizes (although this might be enforced in the future). There are, however, several reasons why file sizes should be kept small:
- In addition to loading the document to be presented (text/html/bitmaps) the Web-client will also have to download the document data-to-be-signed (the original document data).
- As soon as the document data-to-be-signed is downloaded it must also be converted. This process is computationally expensive and can cause the Web-client to freeze for a short while. This is especially true for less powerful platforms like mobile devices.
- In context of mobile devices, using cellular network, file size matter a lot to the overall user experience.
As a rule of thumb the file size of a single document should not exceed 3 MB. But even this will pose a challenge for (older) mobile devices. It is recommended that a document's file size should be kept under 1 MB – smaller file size leads to better user experience.
Merchants should be aware that large PDF files, typically files with a large number of images, might give a less than optimal user experience, especially on mobile devices with limited processing power.