WingArc1st Inc. (Headquarters: Minato-ku, Tokyo; President and CEO: Jun Tanaka; hereinafter "WingArc1st") and Cybertrust Inc. (Headquarters: Minato-ku, Tokyo; President: Yuji Kitamura; hereinafter "Cybertrust") have jointly developed "Trustee eSeal," a digital trust service that proves the issuer of PDF documents, and will begin offering it on June 30, 2026 (Tue). With the widespread adoption of generative AI, the risk of tampering with electronic documents is increasing, with malicious instructions or false information that cannot be visually detected being embedded. For corporate transactions, ensuring authenticity is a crucial element. Against this backdrop, WingArc1st, in collaboration with Cybertrust, has newly developed "Trustee eSeal" to prove the issuer of PDF documents, in addition to "Trustee Timestamp"*1, which proves the existence time of PDF documents. "Trustee eSeal" adopts "iTrust eSeal Certificate"*2 provided by Cybertrust and extends the functionality to apply eSeals to "Trustee," a business form platform. By applying "Trustee eSeal" to a PDF, it is possible to prove "which organization issued it and when." Recipients can verify the issuing company and its corporate number, thus 100% proving the issuer and ensuring the reliability of the electronic document. Furthermore, "Trustee Timestamp" will be provided free of charge to users who contract "Trustee eSeal." By combining proof of "who issued it (Trustee eSeal)" and "when it existed (Trustee Timestamp)," the authenticity of electronic documents can be strongly guaranteed. This service is the result of a collaboration agreed upon in March 2026 to build a digital trust infrastructure for the AI era, promoting the coexistence of legal reliability and operational efficiency in complete paperless inter-company transactions, and realizing a society that utilizes advanced data in line with the AI era.*3 PDFs, eSeals, and timestamps that comply with international standards maintain future compatibility and