Hi
Thank you for using Microsoft Office for IT Professionals Forums.
From your description, It seems impossible to add multiple Electronic signature to the same document.
Office 2007/2010 can let you add multiple digital signatures to the same document.
For 2007
http://technet.microsoft.com/en-us/library/cc545901(office.12).aspx
For 2010
http://technet.microsoft.com/en-us/library/cc545900.aspx
Please take your time to try the suggestions and let me know the results at your earliest convenience. If anything is unclear or if there is anything I can do for you, please feel free to let me know.
Sincerely
William Zhou
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Please remember to mark the replies as answers if they help and unmark them if they provide no help.You might get an invalid signature if the computer from which you are viewing a signed document does not have the root public certificate from which to verify the signer's certificate. Install that onto your computer and it may correct the problem.
Once you edit a file, it will invalidate the signature. The signature is generated such that if one bit of the document's data is flipped, the signature will be invalid and the document can be known to have been modified after its signature.
check this link this may help you out
http://office.microsoft.com/en-us/help/collect-signatures-in-a-document-by-using-a-workflow-HA010220202.aspx
Multiple signatures are possible. Once the first person signs, on the lower left you will see Page: 1 of 1 | Words: 100 | and the red digital signature icon. Click the icon and a signatures box will open on the right.
There will be a requested signatures section which contains the names of those individuals who still need to sign the document. The person clicks their name and signs the document. No need to save the document its done automatically. The next person will do the same thing and no need to save after they do and so on.
No signatures are invalid as others sign.