How to unlock text in InDesign: Master Page items
If you come across an element that is uneditable it is because this element is a Master Page item (something located on Master Page). By default each new document comes with Master Page which you may not realize because it is empty. Any new page you create inside of your document has Master applied to it.
Master Pages can be a huge time-saves and speed up your process. They are great for repetitive elements that have the same attributes on multiple pages. For example, if you have a company logo that will be placed in the top right corner of each page you should not place the logo on each page of your document, you should place it on Master Page instead and apply Master Page to your document pages. This way if you decide to change something (logo file, logo size, logo position, etc.) you can simply update it on one single page and all the other pages that have Master Page applied to it will update automatically across the entire document.
You can have multiple Master Pages and apply different Master Pages to different pages of your document. For example, you can create Master A with company logo and page number and apply it to pages 1-5 and you can create Master B with company slogan and a date and apply it to page 6.
You can view all available Master Pages in pages palette of your template (Window > Pages). In example below you can see 3 Master Pages (A-Master, B-Master, and C-Master). Small letter in a corner of page thumbnail indicates which Master is applied to it. If you would like to apply Master Page to one of your pages simply drag the Master Page icon to a page thumbnail. To apply Master Page to one of your spreads simply drag the Master Page icon to a corner of the spread thumbnail. If you would like to apply Master Page to multiple pages or spreads simply select the page thumbnils to which you want to apply a Master Page then press Alt (Windows) or Option (Mac) and click on Master Page icon.
Anything that you have placed on Master Pages is locked on document pages. Generally you will want to keep those items look to ensure consistency but sometimes you want to locally overwrite some item. To do this you will need to unlock the item first: press Ctrl+Shift (Windows) or Command+Shift (Mac OS) and click the item to unlock it. Once unlocked the item becomes editable. Be careful: this item is now “detached” from Master Page and will not be updated automatically when you change it on Master Page.