Applying digital signature increases PDF Version from 1.5 to 1.6.

Question

I am using Adobe Acrobat Pro 2015.006.30121 in Windows 10.

I need to submit documents with my digital signature to a court. The court uses a program that requires the document to be PDF Version of 1.5 or lower. I save my pdf document using File/Save As Other/Reduced Size PDF. When I look at File/Properties/Document Properties Description the PDF Version is 1.5. However, after I apply my Acrobat digital signature the PDF Version is increased to 1.6. Now the document is uneditable so I cannot do another File/Save As Other to reduce the PDF Version back to 1.5. How do I change a setting such that applying my digital signature does NOT increase the PDF Version?

IsakTen-RwIoo2 · Answer

The features that you need to apply your digital signature do not exist in PDF 1.5. That's why Acrobat increases the version number to match the features it needs. I do not remember which exactly features were introduced in 1.6. I think that SHA2 hash and AES encryption were among the, So, for instance, if your signing certificate uses SHA2 (SHA-256) hash the created signature cannot be opened with 1.5 PDF Viewer. I am not saying that this happen in your case. This just an example of what might've happened.

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