Best way to get signatures for document with fixed layout but different content image.

If I have documents in a template but the content is different, what is the best way for me to get a signature from multiple clients. 

Example: Let's say a document has a custom graph for each client included, however content, placement and even graph size is exactly the same and position. (Just graph image might be slightly different).  

Would I need to upload each document and create a signature box before sending? Is there a better method?