we have signed a PDF using a self-signed certificate (for now) and have told our Adobe Reader X (v 10.1.3) on Windows 7, to trust the signature. Now viewing the signed PDF in Reader X, it nicely shows the message: "Signed and all signatures are valid". So that's good.
Now what we tried, is see whether Reader X would detect tampering: so we've modified the PDF using GoodReader on IPad. Now when we view the PDF in Reader X, it shows "at least one signature requires validating", which kinda is confusing. When opening the signature Panel, and inspecting the certificate details we see it's the original certificate, but then suddenly the earlier message "at least one signature requires validating" changes into the more expected and clear message: "Signed and all signatures are valid, but with unsigned changes after the last signature). Could it be this is some kind of refresh problem in Adobe Reader?