why .pdf files cant sign by using certificate on mobile?

[Gurkan27658265tnpf]

Hi There,

We have an issue with signing the .pdf files by mobile phone in our company. The documents need to sign by different departments. but if an user would like to sign by phone they cant. because acrobat reader mobile does not support signing by certificate. but if the document already signed by previous department they cant sign it by mobile phone signing system. need support on this matter. thanks.

[Gurkan27658265tnpf]

Here is the question;

"How can you sign the documents on mobile which are signed by certificate signature before?"