Here is documentation for developers. User documentation is located at main site.

Parallels Plesk Panel 10	PDF
API RPC Developer’s Guide	890K
API RPC Reference 1.6.3.0	-
XML Schemas	-
Localization Guide	460K
Command Line Reference (Linux)	-
Command Line Reference (Windows)	-

Parallels Plesk Panel 9.5	PDF
PPP 9.5 API RPC Protocol Reference	14M
PPP 9.5 API RPC Protocol Developer Guide	590K
PPP 9.5 Command Line Reference (Linux/Unix)	830K
PPP 9.5 Command Line Reference (Windows)	2.6M
PPP 9.5 Localization Guide (Linux/Unix)	612K
PPP 9.5 Localization Guide (Windows)	631K
PPP 9.5 Backup/Restore CLI Administrator Guide and Reference	790K
PPP 9.5 Migration Guide	575K
PPP 9.5 Modules API Reference	1.3M
PPP 9.5 Modules Developer Guide	617K

Parallels Plesk Panel 9.3	PDF
PPP 9.3 API RPC Protocol Reference	14M
PPP 9.3 API RPC Protocol Developer Guide	590K
PPP 9.3 Command Line Reference (Linux/Unix)	2M
PPP 9.3 Command Line Reference (Windows)	2.4M
PPP 9.3 Localization Guide (Linux/Unix)	612K
PPP 9.3 Localization Guide (Windows)	631K
PPP 9.3 Backup/Restore CLI Administrator Guide and Reference	680K
PPP 9.3 Migration Guide	575K
PPP 9.3 Modules API Reference	1.3M
PPP 9.3 Modules Developer Guide	617K

Parallels Plesk Panel 9.2	PDF
API RPC Protocol Reference	14M
API RPC Protocol Developer Guide	568K
Command Line Reference (Linux/Unix)	780K
Command Line Reference (Windows)	2.2M
Localization Guide (Linux/Unix)	616K
Localization Guide (Windows)	636K
Backup/Restore CLI Administrator Guide and Reference	380K
Migration Guide	324K
Modules API Reference	1.3M
Modules Developer Guide	604K

Parallels Plesk Panel 9.0	PDF
API RPC Protocol Reference	14M
API RPC Protocol Developer Guide	848K
Command Line Reference (Linux/Unix)	2.9M
Command Line Reference (Windows)	3.2M
Localization Guide (Linux/Unix)	312K
Localization Guide (Windows)	336K
Backup/Restore CLI Administrator Guide and Reference	700K
Migrating to Plesk 9.0 Quick Guide	412K

Parallels Plesk Panel 8.6 for Linux/Unix	PDF
API RPC Protocol Developer’s Guide	0.5MB
API RPC Protocol Reference	8.4MB
Localization Guide	0.6MB
Command Line Reference	0.6MB
Modules API Reference	1.3MB
Modules Developer’s Guide	0.6MB
Skins Developer’s Guide	0.7MB

Parallels Plesk Panel 8.6 for Windows	PDF
API RPC Protocol Developer’s Guide	0.5MB
API RPC Protocol Reference	8.4MB
Localization Guide	0.6MB
Command Line Reference	1.5MB
Localization Guide	0.6MB
Skins Developer’s Guide	0.7MB

Parallels Plesk Panel 8.4 for Linux/Unix	PDF
API RPC Protocol Developer’s Guide	0.5MB
API RPC Protocol Reference	8.4MB
Command Line Reference	0.6MB
Localization Guide	0.6MB
Modules API Reference	1.3MB
Modules Developer’s Guide	0.6MB
Skins Developer’s Guide	0.7MB

Parallels Plesk Panel 8.4 for Windows	PDF
API RPC Protocol Developer’s Guide	0.5MB
API RPC Protocol Reference	8.4MB
Command Line Reference	1.5MB
Localization Guide	0.6MB
Developer’s Guide	0.7MB

Parallels Plesk Panel 8.3 for Linux/Unix	PDF
API RPC Protocol Developer’s Guide	0.6MB
API RPC Protocol Reference	8.3MB
Command Line Reference	1.6MB
Localization Guide	0.8MB
Modules API Reference	2.0MB
Modules Developer’s Guide	0.9MB
Skins Developer’s Guide	1.0MB

Parallels Plesk Panel 8.3 for Windows	PDF
API RPC Protocol Developer’s Guide	0.6MB
API RPC Protocol Reference	8.3MB
Command Line Reference	1.5MB
Localization Guide	0.6MB
Skins Developer’s Guide	0.9MB

Parallels Plesk Panel 8.2 for Linux/Unix	PDF
API RPC Protocol Developer’s Guide	0.7MB
API RPC Protocol Reference	8.5MB
Application Vault Reference	0.9MB
Application Vault Developer’s Guide	0.8MB
Command Line Reference	2.4MB
Localization Guide	0.8MB
Modules API Reference	1.5MB
Modules Developer’s Guide	1.8MB
Skins Developer’s Guide	1.0MB

Parallels Plesk Panel 8.2 for Windows	PDF
API RPC Protocol Developer’s Guide	0.7MB
API RPC Protocol Reference	8.5MB
Command Line Reference	2.2MB
Localization Guide	0.9MB
Skins Developer’s Guide	0.9MB

Parallels Plesk Panel 8.1 for Linux/Unix	PDF
API RPC Developer’s Guide	0.7MB
API RPC Reference	14.3MB
Modules Developer’s Guide	0.8MB
Modules API Reference	2.1MB
Application Vault Developer’s Guide	0.8MB
Application Vault API Reference	1.2MB
Skins Developer’s Guide	1.0MB
Localization Guide	0.8MB
Command Line Interface	3.6MB

Parallels Plesk Panel 8.1 for Windows	PDF
API RPC Developer’s Guide	0.7MB
API RPC Reference	14.3MB
Skins Developer’s Guide	0.9MB
Localization Guide	0.8MB
Command Line Interface	0.7MB

Parallels Plesk Panel 8.0 for Linux/Unix	PDF
API Reference
Application Vault Developer’s Guide	0.4MB
Plesk Modules Developer’s Guide	0.6MB
Backup/Restore Utilities User’s Guide	79KB
Integration Handbook	51KB

Parallels Plesk Panel 7.6 for Windows	PDF
CLI Reference	0.3MB
Backup/Restore Utilities User’s Guide	0.2MB

Parallels Plesk Panel 7.5 Reloaded for Linux/Unix	PDF
Complete SDK Documentation

Parallels Plesk Panel 7.5 for Windows	PDF
Complete SDK Documentation
CLI/Advanced Features Reference	0.9MB
Custom Skins Developer’s Guide	0.2MB