You can do what you are asking. But, you will still need some secondary validation from a human before sending it off to the next step.
First, you need to get the box or element around the signature. To do so, you need to find the box… So if the pdf is an image where you can’t highlight any text, then you must use the Find Image of text near the signature box, while scrolling each page until you find the image (preferably starting from the bottom, since the signature is usually near the end). If the pdf is not an image, then you can use Find Text or Find Element; in this situation, you may even be able to find the signature box element. You can also use Anchor Base, however I can’t confirm it’s effectiveness when the element is a signature box.
After, you have the element of the signature box or the element near the signature box, you will want to use the Set Clipping Region to adjust the surrounding box to only include the signature area (use the Highlight activity to help visually see your adjusted box until it is correct). Do some searches on setting the clipping region for syntax on this, because it has been a while since I’ve done this.
Now, that you have a clipping region stored in an element variable, you can then use Get OCR Text using that element. You can even use Save Image, if you would like to insert the image into Excel for the secondary validation. To validate the signature with the bot, you just need to set an array of characters/strings which are identified as invalid such as “”,".",",","/", etc, then use a condition like IF
invalidCharacters.Any(Function(x) x = sigText.Trim), which will be True or False depending on if the OCR text of the signature box has enough there to identify that “something” is there. Note: you will need to play around with the Scale for the OCR engine so it is more accurate.
Anyway, just sharing my experience with this, and hope it helps.