Is there any software for Tablets to edit PDF or PS -files? I am using Samsung galaxy tab 8.9.
Assume you read your lecture materials with your tablet.
You see a mistake. You would like to fix it.
You are using Adobe reader tablet version.

Is there any software by which you can simply add text on PDF or PS -files?
You could give Qoppa PDF Notes a try:

The best app for editing, annotating, filling forms, and signing PDF documents.
qPDF Notes is a user-friendly, all-in-one PDF app to view, edit, and markup PDF documents, digitally sign and share them, and fill PDF forms. Saved documents are fully compatible with Adobe Acrobat and the PDF standard, and can be viewed in any capable PDF reader.

The link leads to the demo (which places a watermark on all your edits); a full version is available for about EUR 4.
If you just want to annotate, there are plenty of apps available capable of that.
P.S.: And it sure is &quot;The best app for editing PDF documents&quot; at the moment -- I could find no other, so it's also the only AFAIK :)