What is the status of an application form for a position that is sent by email? Is the printed signature sufficient?

It is perfectly in order to implement a policy of accepting email or hard copy applications or both and, whichever one the employer chooses to enforce, it should be clearly communicated to potential applicants.

This question really depends on the application process which the employer wishes to adopt. If it is specified that the employer will accept emailed applications, then this should be sufficient. As long as the application process is applied fairly and consistently, no issues should arise.