When Inventor open a AutoCAD file with blocks, how can I replace those block insertions with my own sketch(or parts) and delete block definitions(sketched symbols)? Or any better idea to do the work?

You can troubleshoot crashes in AutoCAD with the following methods:

• Update and verify the latest version.
• Update the operating system you are using.
• Turn off Hardware Acceleration.
• Update your graphic drivers.
• Repair and reinstall autocad.

To write text in AutoCAD LT go to the home tab. Then go to Multiline Text under the Annotation panel. Now state the opposite corners of the bounding box and define the multiline width of text object. In the now displayed Text Editor contextual tab, enter the text. To transform the text, select and highlight it then specify the formatting changes. Lastly, save the changes and exit the editor.

Yes, AutoCAD LT offer an isometric drawing tool for creating isometric drawings.

Yes, you can upgrade AutoCAD LT to full version. To upgrade you will require an upgrade license and Upgrades of LT are about USD 325 per seat.

For AutoCAD LT you require at least 8 GB RAM, but 16 GB is recommended.