If you need to draw on a map or diagram as part of your As-built updates, you can do so by downloading a PDF of the desired file from the Work Item, then uploading your edited copy to the Field Report for that Work Item when you fill it out.
If you do this often, ensure the Work Items in question always have a design attached either to them, or their parent Work Order or Work Package.
Open the desired Work Item in the Work page, and tap "See All" on the "Files" section to open the file viewer. Select the appropriate file from the list; if the file is under the Work Order or Work Package, you'll need to go to its folder to see the file.
When you have the right file open, tap the "Share" button to bring up a list of options. Select the option which lets you open the file in your desired PDF editor (different options will be available depending on your operating system).
Choose your desired PDF file editor from the list (see image in step 2), and Vitruvi™ will download a copy of the file to your device, then open it in the program you chose. You may now edit the PDF in this viewer.
After adding any redlines or other notes in your PDF editor, you'll need to re-upload the file to the Work Item through a Field Report. Follow the steps in the Field Reports tutorial to create and fill out a field report. Then, tap the "file" area, and choose "upload a file".
Select the PDF file you just edited, and upload it to the Field Report.
Now when you submit the field report, the PDF will be attached to it (see below).